Final answer:
The statement suggesting a single, specified concentration of slaked lime and soda ash for all water treatments aiming for maximum softness is false. The required concentration of these chemicals is based on the specific water's initial hardness and chemistry.
Step-by-step explanation:
The concentration of slaked lime [Ca(OH)2] required to treat water for maximum softness cannot be universally specified as it depends on the initial hardness of the water. However, the concentration of slaked lime is calculated based on the amount needed to react with the calcium and magnesium ions to form precipitates, which can then be filtered out of the water. The same principle applies to the addition of soda ash (Na2CO3), where it is used to remove divalent cations by precipitation. The actual amounts to be used are dependent on the water chemistry and the desired final water hardness.
Lime softening process effectively reduces water hardness by raising pH with calcium hydroxide, facilitating the precipitation of calcium as CaCO3 and magnesium as Mg(OH)2. The false statement that there is a single concentration of slaked lime and soda ash to achieve maximum practical softness is because water characteristics can substantially vary, necessitating different quantities for treatment.