Identify the principal causes of acidity in water supplies (choose the most complete statement).
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AMineral acids only
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BFree carbon dioxide only
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CIron sulphate and aluminium sulphate only
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DAll of the above
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ENone of these
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Acidity in water is due to free mineral acids, dissolved carbon dioxide, and hydrolyzing metal salts that generate acidic species. Understanding sources helps in choosing appropriate neutralization or corrosion-control strategies.
Given Data / Assumptions:
- Typical raw waters and chemically treated waters (e.g., alum coagulation).
- Standard definition of acidity as the capacity to neutralize bases.
Concept / Approach:Free CO2 forms carbonic acid in water. Mineral acids (e.g., H2SO4, HCl) directly contribute to acidity. Certain metal salts (FeSO4, Al2(SO4)3) hydrolyze to produce acidic conditions (e.g., forming H+ via hydrolysis), increasing acidity until alkalinity neutralizes them.
Step-by-Step Solution:
List recognized contributors to acidity: mineral acids, free CO2, hydrolyzing metal sulphates.Evaluate the options for completeness.Choose the comprehensive option: 'All of the above'.Verification / Alternative check:Standard water chemistry texts describe titratable acidity components including CO2 and hydrolysis products of alum/iron salts.
Why Other Options Are Wrong:
- Each partial listing omits other well-known contributors to acidity; therefore incomplete.
Common Pitfalls:
- Equating acidity solely with free mineral acids and ignoring CO2 or salt hydrolysis.
Final Answer:All of the above