Transition Metals (DONE)

Question 1

What is the definition of a transition metal?

Answer 1

D-block elements that form at least one stable ion or stable positive oxidation state with a partially filled d-subshell.

Question 1

What are the characteristics of transition metals?
(5 marks)

Answer 1

• High melting/boiling points
• Coloured compounds
• Complex ions
• Variable oxidation states
• Good catalysts

Question 2

Why are Scandium (Sc) and Zinc (Zn) not transition metals?
- Show the electron arrangements of the ions they form
(3 marks)

Answer 2

• They do not form stable ions with partially filled d-subshells
• Sc [Ar] 4s² 3d¹ => Sc³⁺ [Ar]
• Zn [Ar] 4s² 3d¹⁰ => Zn²⁺ [Ar] 3d¹⁰

Question 3

How do transition metals have variable oxidation states?
(2 marks)

Answer 3

• 4s and 3d subshells have energy levels very close to one another
• Different number of electrons can be gained or lost using similar amounts of energy

Question 4

Give the colour of the following ions:
- Cr³⁺
- Fe³⁺
- CrO₄²⁻
- Co²⁺
- Fe²⁺
- Cr₂O₇²⁻
- MnO₄⁻

Answer 4

• Cr³⁺ GREEN
• Fe³⁺ YELLOW
• CrO₄²⁻ YELLOW
• Co²⁺ PINK
• Fe²⁺ PALE GREEN
• Cr₂O₇²⁻ ORANGE
• MnO₄⁻ PURPLE

Question 5

What are ligands?
- Give examples of ligands

Answer 5

Species with a lone pair of electrons/donate a pair of electrons which can form a coordinate bond with a central metal ion
- Cl⁻, NH₃, H₂O

Question 6

What is the systematic name/alternative names of [Cu(H₂O)₆]²⁺ and what is its shape. What bond angle is present?
(3 marks)

Answer 6

• Hexaaquacuprate (II) or Cu²⁺ (aq)
• Octahedral Complex Ion
• 90ᵒ

Question 7

What is the systematic name of [CuCl₄]²⁻, what is its shape and what bond angle is present?
(3 marks)

Answer 7

• Tetrachlorocuprate (II)
• Tetrahedral Complex Ions
• 109.5ᵒ

Question 8

What are the colours of the following complex ions:
- [Cu(H₂O)₆]²⁺
- [Co(H₂O)₆]²⁺
- [Fe(H₂O)₆]²⁺
- [CuCl₄]²⁻
- [CoCl₄]²⁻
- [Cu(NH₃)₄(H₂O)₂]²⁺
- [Fe(H₂O)₆]³⁺
- [Cr(H₂O)₆]³⁺

Answer 8

• [Cu(H₂O)₆]²⁺ PALE BLUE
• [Co(H₂O)₆]²⁺ PINK
• [Fe(H₂O)₆]²⁺ PALE GREEN
• [CuCl₄]²⁻ YELLOW/OLIVE GREEN
• [CoCl₄]²⁻ BLUE
• [Cu(NH₃)₄(H₂O)₂]²⁺ ROYAL BLUE
• [Fe(H₂O)₆]³⁺ YELLOW
• [Cr(H₂O)₆]³⁺ DARK GREEN

Question 9

How are transition metals able to form coloured compounds?
(5 marks)

Answer 9

• When ligands form a coordinate bond with a transition metal ion
• There is repulsion of electrons from ligands and the electrons in the d-orbitals of the metal ion
• The 3d orbitals split into 2 higher and 3 lower energy levels
• Electrons are able to jump from lower to higher split 3d orbitals and this requires energy absorbed from visible light
• Remaining light is reflected and observed by the human eye

Question 10

Give the following formulas of the equation with hydroxide ions and state the colour of the product formed.
- [Cu(H₂O)₆]²⁺
- [Fe(H₂O)₆]²⁺
- [Fe(H₂O)₆]³⁺
- [Cr(H₂O)₆]³⁺

Answer 10

• Cu(H₂O)₄(OH)₂ / Cu(OH)₂ PALE BLUE PPT
• Fe(H₂O)₄(OH)₂ / Fe(OH)₂ DIRTY GREEN PPT
• Fe(H₂O)₃(OH)₃ / Fe(OH)₃ RED BROWN PPT
• Cr(H₂O)₃(OH)₃ / Cr(OH)₃ GREY GREEN PPT
• [Cr(OH)₆]³⁻ BOTTLE GREEN AQUEOUS

Question 11

What is a catalyst?

Answer 11

Speeds up the rate of reaction without being used up. It provides an alternative reaction pathway with a lower activation energy.

Question 12

What is adsorption (solid catalysts)?
(2 marks)

Answer 12

• Solid catalysts work by adsorbing molecules onto an active site on the surface of the catalyst.
• Active sites increase proximity of molecules and weaken the covalent bonds so that rate of reaction is increased

Question 13

Give an example of ligand change where the coordination ion number does not change and where it does change.
- Give reasons for why both happen

Answer 13

• [Co(H₂O)₆]² + 6NH₃ -> [Co(NH₃)₆]²⁺ + 6H₂O
  PINK STRAW YELLOW
  NH₃ and H₂O are similar in size and both uncharged
• [Cu(H₂O)₆]²⁺ + 4Cl⁻ -> [CuCl₄]²⁻ + 6H₂O
  PALE BLUE YELLOW
  the Cl⁻ ligand is bigger than H₂O and is charged therefore substitution will result in a change in coordination number. Takes place when HCl is present.