Developing Metals

Question 1

Give the electron configuration of a Colbalt and Chromium atom, using noble gas cores

Answer 1

• Co > [Ar] 4s2 3d7
• Cr > [Ar] 4s1 3d5
(Chromium and copper are anomalies!)

Question 2

When forming ions in the transition metals, electrons from which subshell are lost first?

Answer 2

The 4s subshell

Question 3

Given that MnO4- can be reduced to Mn2+ and C2O4 can be oxidised to CO2, write the full ionic equation for the redox reactions between permanganate (VII) and ethanedioate ions

Answer 3

2MnO4- + 16H+ + 5C2O4 > 2Mn2+ + 10CO2 + 8H2O

Question 4

What is a ligand?

Answer 4

A ligand is an anion or neutral molecule with a lone pair of electrons which it can donate to a central metal ion, forming a dative covalent bond

Question 5

What is the coordination number of a complex ion?

Answer 5

The number of dative bonds around the central metal ion

Question 6

Draw the formula of the complex ion formed from hydrating Cu2+, stating its coordinate number, shape, and drawing dashed lines where applicable

Answer 6

• Cu central metal ion (without 2+ charge!)
• Lone pair on 6 oxygens of 6 waters pointing towards the Cu
• 6 dative bonds pointing towards Cu from lone pairs
• Entire ion in square brackets with 2+ outside
• Octahedral with coordination number of 6

Question 7

Give/draw two bidentate ligands

Answer 7

• 1,2-diaminoethane (H2N-CH2-CH2-NH2)
• Ethanedioate ion
(C2O4)2-

Question 8

State the name of the main hexadentate ligand, and explain what a polydenatte ligand means

Answer 8

• EDTA
• A ligand that forms MORE THAN ONE (NOT multiple!) dative bonds to the central metal ion

Question 9

What does a change in coordination number signify during a ligand substitution reaction?

Answer 9

A drastic/big change in colour

Question 10

What happens to (Cu(H2O)6)2+ upon addition of excess ammonia solution?

Answer 10

A ligand substitution reaction: (Cu(NH3)4(H2O)2)2+ is formed and the colour changes from blue to deep blue-violet

Question 11

What are the verbs used for colour being seen from a TM solid and an aqueous TM solution

Answer 11

Solid: The solid is REFLECTING colour
Aqueous: The solution is TRANSMITTING colour

Question 12

Explain the origin of colour in complex ions

Answer 12

• d-orbitals in the metal ion are split by the ligands, creating an energy gap
• Light is absorbed when electrons are excited with energy equivalent to the energy gap (ΔE=hν)
• The colour results from frequencies of light that are not absorbed

Question 13

Explain why the colours of transition metal complexes varies with different ligands

Answer 13

• Ligands around the central metal ion cause the d-orbitals to split in energy
• Different ligands are better/worse at donating lone pairs so create larger/smaller energy gaps
• The coordination number and shape of the ligand can cause the orbitals to split differently (tetrahedral splits the orbitals differently to octahedral as the ligands point in different directions)

Question 14

Give the complex ion formed from the hydration of Fe2+

Answer 14

[Fe(H2O)6]2+

Question 15

Give the complex ion formed from the hydration of Fe3+

Answer 15

[Fe(H2O)6]3+

Question 16

Give the complex ion formed between Cu2+ and sodium ethanedioate

Answer 16

[Cu(C2O4)3]4-

Question 17

Give the complex ion formed between Cu2+ and Cl-, stating the colour

Answer 17

• [CuCl4]2-
• Lime green

Question 18

Give an example of a hexadentate ligand and draw the complex ion it forms with Cu2+

Answer 18

• EDTA
• [Cu(EDTA)]2-

Question 19

Explain why adding ammonia solution to a solution containing Cu2+ causes a blue precipitate to form

Answer 19

• Ammonia in ammonia solution reacts with water to produce NH4+ and OH-
• OH- can react with Cu2+ to form a blue ppt of Cu(OH)2