Question
Calculate hardness in units of mg/l as CaCO$_3$ of a ground water sample having Ca$^{++}$ ion concentration of 100 mg/l.
The correct answer is
250
Calculate Groundwater Hardness as CaCO3
Groundwater hardness is commonly expressed in terms of the equivalent concentration of calcium carbonate (CaCO3). To calculate hardness from the concentration of specific ions like Ca++, a conversion factor based on their equivalent weights is used.
Determine Conversion Factor
The conversion factor is the ratio of the equivalent weight (EW) of CaCO3 to the EW of the ion (Ca++ in this case).
- Equivalent Weight (EW) = Molecular Weight (MW) / Valence (n)
- EW of CaCO3 = (100.09 g/mol) / 2 = 50.05 g/eq
- EW of Ca++ = (40.08 g/mol) / 2 = 20.04 g/eq
- Conversion Factor =
$ \frac{EW_{CaCO_3}}{EW_{Ca^{++}}} $ - Conversion Factor =
$ \frac{50.05 \text{ g/eq}}{20.04 \text{ g/eq}} \approx 2.5 $
Calculate Total Hardness
Multiply the concentration of the ion by the conversion factor to get the hardness expressed as CaCO3.
- Hardness (as CaCO3) = [Ca++] (in mg/l) × Conversion Factor
- Hardness (as CaCO3) = 100 mg/l × 2.5
- Hardness (as CaCO3) = 250 mg/l
Therefore, the hardness of the groundwater sample is 250 mg/l as CaCO3.
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Important Questions from Water Treatment
- Choose the correct statements about coagulation process.
A. Coagulation makes smaller colloids to adhere to each other to form large floc particles
B. Colloids are continually involved in Brownian moment.
C. Colloids are stable because of their surface charge.
D. Coagulants are preferably trivalent cations.
E. Coagulants are soluble in neutral pH.
Choose the most appropriate answer from the options given below: - Hardness of water is due to the presence of
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Diameter = 50m, Depth = 2.5m, average detention time = 2 hours.
How much quantity of waste water is being treated ? - Choose the correct statements
A. Temperature has a effect in disinfection treatment of water.
B. pH controls the amount of HOCl and OCl in water.
C. Cl$_2$ gas used for disinfection forms HCl as a product in water.
D. Disinfection action is because of HOCl formed and not due to Cl$_2$ gas.
E. Combined chlorine exist in water due to combination of HOCl with NH$_3$ and organic compounds.
Choose the correct answer from the options given below:
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