Question 1

Why do coordination compounds help in metal extraction?

Accepted Answer

Ligands bind selected metal ions to form soluble or precipitable complex ions. In this example, cyanide converts gold into soluble [Au(CN)₂]⁻, after which zinc can displace it as solid gold.

Question 2

What are the coordination numbers of gold and zinc in the two complex ions?

Accepted Answer

Gold has coordination number 2 in linear [Au(CN)₂]⁻, while zinc has coordination number 4 in tetrahedral [Zn(CN)₄]²⁻. Each CN⁻ ligand is monodentate, so its denticity is 1.

Question 3

Which metal is oxidised during cementation?

Accepted Answer

Zinc is oxidised from oxidation state 0 to +2. Gold leaves the complex ion as neutral Au metal, where its oxidation state is 0.

Question 4

What is Wilkinson’s catalyst in this experiment?

Accepted Answer

RhCl(PPh₃)₃ is a soluble molecular rhodium catalyst. It reacts through molecular Rh intermediates with an alkene and H₂, forms the saturated alkane and is regenerated without overall consumption.

Question 5

What does it mean when a catalyst is regenerated?

Accepted Answer

The catalyst may form temporary molecular intermediates while the reaction proceeds, but after the cycle it returns to its original state. It speeds the reaction and is not consumed in the overall equation.

Question 6

How does Wilkinson’s catalyst change a reaction pathway?

Accepted Answer

It provides a molecular Rh pathway for hydrogenation of an alkene with H₂. Temporary coordination and Rh–H intermediates lead to the saturated alkane, after which the catalyst is recovered.

From Ore to Catalyst: Coordination Compounds at Work

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