Answer: Slaked lime Ca(OH)2 to remove temporary hardness by precipitating CaCO3.
- A Slaked lime Ca(OH)2 to remove temporary hardness by precipitating CaCO3
- B Washing soda (Na2CO3) to precipitate both temporary and permanent hardness
- C A synthetic ion exchange resin that swaps Ca2+ for Na+
- D Alum, which coagulates suspended colloidal clay particles
Correct answer: A. Slaked lime Ca(OH)2 to remove temporary hardness by precipitating CaCO3
Explanation: Clark's method adds just enough lime to convert soluble bicarbonates to insoluble carbonates: Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O.
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.