Answer: Sodium aluminium silicate (zeolite/permutit) ion exchanger.
- A Sodium aluminium silicate (zeolite/permutit) ion exchanger
- B Activated charcoal that adsorbs dissolved calcium and magnesium ions
- C A combined lime-and-soda treatment to precipitate both hardness types
- D Simple distillation to vaporise and recondense the pure water
Correct answer: A. Sodium aluminium silicate (zeolite/permutit) ion exchanger
Explanation: Permutit (zeolite, Na2Al2Si2O8) exchanges Na+ ions for Ca<sup>2+</sup> and Mg<sup>2+</sup> hardness ions, softening the water.
Each water molecule's O-H bonds (covalent, solid) can hydrogen-bond (dashed) to neighbouring molecules, forming an extended network responsible for water's unusually high boiling point and density anomaly.
Concept context
The simplest and most abundant element in the universe. Study its unique position in the periodic table, isotopes (protium, deuterium, tritium), properties of water and hydrogen peroxide, and industrial uses.