Aqueous Inorganic compounds and TM

Question 1

Substitution reaction definition

Answer 1

replacement of one ligand by another

Question 2

Lewis acid and base

Answer 2

L Acid: electron pair acceptor

L Base: electron pair donor

Question 3

Why is [Co(Y)₃]²⁺ more stable than [Co(X)₆]²⁺

Answer 3

• Entropy change for reaction is positive as there is more disorder
• 4 mol reactants form 7 mol products
• Bidentate ligand replaces unidentate

Question 4

Amphoteric

Answer 4

behaves as both acids and bases

Question 5

What is meant by the acidity of metal aqua ion

Answer 5

• O–H from H₂O broken
• H+ formed

Question 6

How do water ligands form bonds with a TM

Answer 6

• O in H2O has a lone pair of electron
• This pair is donated to the TM

Question 7

How does changing the ligand change the colour of a solution?

Answer 7

• In different complexes the d orbitals have different energies. The d orbital splitting will be different
• So a different frequency (colour) of light is absorbed to excite the d electrons
• Consequently a different frequency (colour) of light is transmitted

Question 8

Explain why the products of Cr²⁺ and Cr³⁺ reacting with CO₃^2- are different

Answer 8

• With [Cr(H₂O)₆] ²⁺ get CrCO₃
• with [Cr(H₂O)₆] ³⁺ get Cr(H₂O)₃(OH)₃ AND CO2
• Cr³⁺ differs from Cr²⁺ because it forms H+ ions
• As Cr³⁺ polarises water
• Cr³⁺ has a greater charge density

Question 9

Why is a transition metal solution coloured?

Answer 9

• One colour (frequencies) of VISIBLE lighjt is absorbed
• This is to excite D electrons
• The remaining frequency is transmitted through the solution and absorbed

Question 10

Why is Co₂SO₄ red?

Answer 10

• Blue light is absorbed from white light
• Due to D electrons moving to higher energy levels (excitation)
• Red light that remains is transmitted and is observed

Question 11

Nucleophile definition

Answer 11

• Species that donates a pair of electrions
• Lewis base

Question 12

Give 3 reasons why something can be classified as a catalyst

Answer 12

• Alternative route with lowers activation energy
• Chemically changed (regenerated)
• Speeds up reaction

Question 13

Chelate effect definition

Answer 13

• substitution of a monodentate ligand by multidentate ligand
• a more stable molecule is formed
• There is an increase in Entropy

Question 14

Why can complexes with Cl- ligands only have tetrahedral structures and not octahedral?

Answer 14

• Cl- is a lot bigger than H₂O ligands
• Only 4 can fit around
• Cl- negatively charged so would repel

Question 15

You have 1 mol/dm³ of Fe³⁺ ions and a colourimeter. How would you determine the conc of Fe³⁺ in an unknown solution

Answer 15

• Add OH^- ligands to intensify colour
• Make up solutions of known concentrations
• Measure absorbances of known concentrations
• Plot a calibration curve
• Measure absorbance of unknown concentration
• Compare with calibration curve

Question 16

Explain why different catalysts have different activities

Answer 16

• If adsorption is too weak then reactants and held long enough for them to collide
• If adsorption is too strong then the products dont desorb

Question 17

Convert [Cr(OH)₆]^3- to CrO₄^2-

Answer 17

• NaOH and H₂O₂
• [Cr(OH)₆]^3- + 2OH- → CrO₄^2- + 4H₂O + 3e-

Question 18

Co²⁺ cannot easily be oxidised to cobalt(III) ions in water. Suggest why this oxidation can be carried out in aqueous ammonia and identify a suitable oxidising
agent.

Answer 18

• [Co(NH3)6]²⁺ formed by reaction with NH₃
• Complex easy easier to oxidise
• H₂O₂ (or oxygen)