Question

Which one of the following process will produce hard water?

• A. Saturation of water with ${\mathrm{CaSO}}_4$
• B. Addition of ${\mathrm{Na}}_2{\mathrm{SO}}_4$ to water
• C. Saturation of water with ${\mathrm{CaCO}}_3$
• D. Saturation of water with ${\mathrm{MgCO}}_3$

Answer 1

The correct option is A

Saturation of water with ${\mathrm{CaSO}}_4$

Explanation for correct option

(A) Saturation of water with ${\mathbf{CaSO}}_{\mathbf{4}}$

Hard water

• When water percolates through calcium and magnesium carbonates, bicarbonates, and sulfates found in limestone, chalk, or gypsum, hard water is produced.
• It may be extremely challenging in industrial settings where water hardness is controlled to prevent expensive failures in cooling towers, boilers, and other water-handling equipment.
• In domestic settings, hard water is frequently identified by the absence of foam that forms when soap is stirred in water and by the buildup of limescale in kettles and water heaters.

Saturation of water with ${\mathbf{CaSO}}_{\mathbf{4}}$

• Rain that has dissolved carbon dioxide can carry calcium ions away.
• Stalactites and stalagmites may form as calcium carbonate re-deposits as calcite as carbon dioxide is released into the environment.
• Calcium and magnesium ions can occasionally be eliminated by water softeners.
• Permanent hardness is frequently difficult to remove by boiling.
• The cause is typically the presence of minerals in the water, such as calcium sulfate/calcium chloride and magnesium sulfate/magnesium chloride, that do not precipitate away as the temperature increases.
• Ions that cause water to become permanently hard can be eliminated using a water softener or an ion-exchange column.

Explanation for incorrect options

• Saturation of water with ${\mathrm{CaSO}}_4$ produce hard water.
• Hence, all other options (B), (C), and (D) are incorrect.

Therefore, the correct option is (A) Saturation of water with ${\mathbf{CaSO}}_{\mathbf{4}}$.