Section 10 Developing Metals

Question 1

How does rusting occur?

Answer 1

Iron exposed to oxygen and water results in Fe²+ and OH-

These Fe²+ and OH- combine ro form precipitate of iron (ii) hydroxide, Fe(OH)
2

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

Iron (iii) hydroxide gradually turns into hydrated Iron (iii) oxide, Fe2O3.xH2O this is rust.

Question 2

Ways to prevent rusting

Answer 2

1. Painting or coating with a polymer.
2. Oiling/ greasing for moving parts like bike chains.
3. Sacrificial method: involves placing a more reactive metal with the iron. The water and oxygen then react this instead of the iron.

Question 3

Rules for transition metal configuration?

Answer 3

4s orbital fills up first

3d orbitals occupied singly at first. Double up when have to.

Chromium likes to have prefers to have one electron in 4s to give stability

Copper prefers to have full 3d orbital and just one electron in 4s for stability.

Question 4

Why are scandium and zinc not transition metals?

Answer 4

1. Scandium only forms one ion, Sc3+ which has empty d sub shell.
2. Zinc only forms one ion, Zn²+, which has a full d sub-shell.

When ions are formed the s electrons are removed first

Question 5

Properties of transition metals?

Answer 5

1. Transition metals can exist in variable oxidation states.
2. Form coloured ions in solution.
   Fe²+ are pale green, Fe³+ ions are yellow.
   Cu²+ ions are blue

Question 6

Define ligand?

Answer 6

A species that donates a pair of electrons to a central transition metals ion form a coordinate (dative covalent) bond.

Question 7

How do ligands split the 3d sub shell into 2 energy levels?

Answer 7

1. Normally the 3d orbital in transition metal ions all have same energy. But when ligand come along and bond to the ions, some of the orbitals gain energy. Splitting 3d orbital into two different energy levels.
2. Electrons tend to occupy lower orbitals. To jump up to higher orbitals they need energy equal to energy gap this energy comes from visible light.
3. The amount of energy needed to make electrons jump depends upon central metal ion, oxidation state, ligand, Coordination number. Because they affect size of energy gap.

Colours of compounds complementary to those they absorbed.

Question 8

Transition metal hydroxides?

Answer 8

When you mix an aqueous solution of transition metal ions with aqueous NaOH.

In aqueous solutions transition metals take form [M(H2O)6]n+

Copper ii: goes from pale blue solution to a blue precipitate.

Iron ii: goes from a pale green solution to a green precipitate which darkens on standing.

Iron iii: goes from a yellow solution to an orange precipitate which darkens on standing

Question 9

Ligand substitution?

Answer 9

Ligands can exchange places with one another.

If Ligands of similar size, then the coordination number of complex doesn’t change.

If ligands are different sizes Coordination number and shape change.

Sometimes substitution is only partial.

Question 10

Hydrogen cyanide will react with carbonyls by nucleophilic addition.

Answer 10

Hydrogen cyanides a weak acid- partially dissociates in water to form H+ ions and CN-

1. the CN- groups attacks the partially positive carbon atom and donates a pair of electrons.
2. H+ bond to oxygen to form hydroxyl group.