Water Quality Parameters MCQ with answer and solution

Concept

Carbonate and Non-Carbonate Hardness

Formula

Carbonate Hardness = Minimum(Total Hardness, Total Alkalinity)

Step-by-step solution

1. Review the given question regarding methyl orange alkalinity and total hardness. 2. Recall the relationship: Carbonate Hardness = Minimum(Total Hardness, Total Alkalinity). 3. Since Total Alkalinity equals or exceeds Total Hardness, all of the hardness is Carbonate Hardness, so select Option (b).

Explanation

When total alkalinity (methyl orange alkalinity) equals or exceeds total hardness, there are enough carbonate and bicarbonate ions to chemically pair with all the hardness-causing calcium and magnesium ions. As a result, all the hardness in the water is carbonate hardness, and non-carbonate hardness is zero.

Shortcut

To remember the relationship between Total Hardness (TH) and Total Alkalinity (TA), use the rule "CH is always the smaller value (CH = Min)": - If Alkalinity ≥ Total Hardness: All hardness is Carbonate Hardness (CH = TH, NCH = 0). - If Total Hardness \> Alkalinity: Carbonate Hardness equals Alkalinity (CH = TA), and the remaining balance is Non-Carbonate Hardness (NCH = TH - TA).

Common mistake

A common mistake is selecting option A (non-carbonate hardness) by incorrectly assuming that when alkalinity is greater, the remaining balance represents non-carbonate hardness. In reality, non-carbonate hardness only exists when total hardness exceeds total alkalinity; when alkalinity equals or exceeds total hardness, non-carbonate hardness becomes zero and all hardness is strictly carbonate hardness.