Question

If the total hardness and alkalinity of a sample of water are 300 mg/L and 100 mg/L (CaCO₃ scale) respectively, then its carbonate and non – carbonate hardness (in units of mg/L) will be respectively.
1. 100 and 200
2. 400 and 300
3. 100 and 400
4. 400 and zero

Answer 1

Correct Answer - Option 1 : 100 and 200

Concept:

Case 1: If Total hardness is greater than Total alkalinity

Carbonate hardness = Total alkalinity and Non-carbonate hardness = Total hardness - Carbonate Hardness

Case 2: If Total hardness is less than Total alkalinity

Carbonate hardness = Total hardness and Non-carbonate hardness = 0 (zero)

Calculation:

Given,

Total hardness = 300 mg/l

Alkalinity = 100 mg/l

Here, Total hardness > Alkalinity, Case 1 follows,

Carbonate hardness = alkalinity = 100 mg/l

Non - carbonate hardness = Total hardness – Alkalinity

Non - carbonate hardness = 300 – 100 = 200 mg/l