26.2 A2 Level

Homogeneous and heterogeneous catalysts

10 flashcards to master this topic

Definition Flip

Define a homogeneous catalyst and provide an example.

Answer Flip

A homogeneous catalyst is in the same phase as the reactants.

Example: Atmospheric oxides of nitrogen in the oxidation of atmospheric sulfur dioxide (both gases).
Key Concept Flip

Explain the mode of action of a heterogeneous catalyst, including the key steps.

Answer Flip

Heterogeneous catalysts work via adsorption of reactants onto the catalyst surface, weakening of reactant bonds, reaction on the surface, and desorption of products. An example is iron in the Haber process.

Key Concept Flip

Why do transition elements exhibit variable oxidation states?

Answer Flip

Transition elements have variable oxidation states due to the small energy difference between the 3d and 4s sub-shells. This allows for the loss of varying numbers of electrons from these sub-shells.

Definition Flip

Define a ligand, and give two examples of monodentate ligands.

Answer Flip

A ligand is a species that contains a lone pair of electrons that forms a dative covalent bond to a central metal atom/ion. Examples of monodentate ligands include H₂O and NH₃.

Key Concept Flip

Describe the geometry of a [Cu(H₂O)₆]²⁺ complex ion.

Answer Flip

The [Cu(H₂O)₆]²⁺ complex ion has an octahedral geometry. This means the central copper(II) ion is surrounded by six water ligands, with bond angles of 90°.

Key Concept Flip

Explain why transition elements can act as catalysts.

Answer Flip

Transition elements act as catalysts because they have more than one stable oxidation state and vacant d orbitals. These orbitals can form dative bonds with reactants, facilitating bond formation and/or weakening.

Definition Flip

What is a complex ion, and how is it formed?

Answer Flip

A complex ion is formed by a central metal atom/ion surrounded by one or more ligands. These ligands attach via dative covalent bonds utilizing the metal ion's vacant d orbitals.

Key Concept Flip

Describe the colour change when excess ammonia is added to a solution of copper(II) ions.

Answer Flip

Initially, adding ammonia to copper(II) ions forms a pale blue precipitate of copper(II) hydroxide. Adding excess ammonia dissolves the precipitate, forming a deep blue solution of the tetraamminecopper(II) complex, [Cu(NH₃)₄(H₂O)₂]²⁺.

Definition Flip

Define a transition element.

Answer Flip

A transition element is defined as a d-block element which forms one or more stable ions with incomplete d orbitals.

Key Concept Flip

What is ligand exchange and give an example with copper(II) ions.

Answer Flip

Ligand exchange is the replacement of one ligand by another in a complex.

Example: adding concentrated HCl to [Cu(H₂O)₆]²⁺ replaces the water ligands with chloride ligands, forming [CuCl₄]²⁻ which is yellow-green.

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