Nature of science:

Risks and problems—scientific research often proceeds with perceived benefits in mind, but the risks and implications also need to be considered. (4.8)

• Toxic doses of transition metals can disturb the normal oxidation/reduction balance in cells through various mechanisms.
• Some methods of removing heavy metals are precipitation, adsorption, and chelation.
• Polydentate ligands form more stable complexes than similar monodentate ligands due to the chelate effect, which can be explained by considering entropy changes.

Applications and skills:

• Explanation of how chelating substances can be used to remove heavy metals.
• Deduction of the number of coordinate bonds a ligand can form with a central metal ion.
• Calculations involving K_sp as an application of removing metals in solution.
• Compare and contrast the Fenton and Haber–Weiss reaction mechanism

. Guidance:

• Ethane-1,2-diamine acts as a bidentate ligand and EDTA^4- acts as hexadentate ligand.
• The Haber–Weiss reaction generates free radicals naturally in biological processes. Transition metals can catalyse the reaction with the iron-catalysed (Fenton) reaction being the mechanism for generating reactive hydroxyl radicals.
• K_sp values are in the data booklet in section 32.

• What responsibility do scientists have for the impact of their endeavours on the planet?

Utilization:

• Syllabus and cross-curricular links:
• Topic 9.1—redox reactions
• Topic 13.2—transition metal complexes
• Biology option C.3—impact of humans on ecosystems

Aims:

• Aims 1 and 8: Investigations of waste water treatment.
• Aim 6: Experiments could include investigations of K_sp.