Question

Explain how the diphosphate ion, [O₃P−O−PO₃]⁴−, can function as a water softener that prevents the precipitation of Fe2+ as an insoluble iron salt.

Answer 1

The diphosphate ion functions as a water softener by forming soluble complexes with Fe²⁺ ions, which prevents their precipitation as insoluble iron salts and mitigates the effects of hard water.

Step-by-step explanation:

The diphosphate ion, represented by the formula [O₃P-O-PO₃]⁴⁻, known chemically as pyrophosphate, serves as an effective water softener by forming complexes with metal ions like Fe²⁺. The formation of these complexes prevents Fe²⁺ from precipitating out of solution as insoluble iron salts.

This process is important because the precipitation of metal ions can lead to the undesirable effects such as bathtub rings or gray tinges on clothing caused by 'hard' water. The process of preventing precipitation relies on the complexing agent's ability to bind with metal ions, which increases the equilibrium constant for complex-ion formation.

This makes the complexed metal ions more soluble in water, thereby keeping them dissolved and avoiding precipitation.