Determination of Water Hardness

Theoretically water hardness means the concentrations of all the metallic cations except the cations of the alkali metals. All nonmetallic ions like Hydrogen ion are excluded from the definition. Normally in the largest part waters, all off the water hardness is occurred by reason of the presence of calcium and magnesium ions. But in some water it should be consideration the measurable concentration of iron, zinc, manganese, aluminum, strontium and other metals. The water hardness is expressed as equivalent concentration of calcium carbonate.





There are different methods for determination of water hardness; following three methods are major:

(i) Hardness by calculation,

(ii) Soap titration method and

(iii) Compleximetric or EDTA titration method.

Hardness by calculation

Hardness by calculation is taking into consideration the most accurate method for determination of water hardness. This method is appropriate to all waters. In this method at first we have to analysis the concentration of calcium and magnesium cations. Then we have to analysis the other hardness producing cations, if their amount is significant. After that the total result is express as equivalent calcium carbonate concentration.

To obtain equivalent calcium carbonate concentration, it should be multiple the concentration of each water hardness producing cations separately by the proper factor. By together all the consequence we get our final result of sample water. Following are the proper factor for determination of water hardness for different cations.

Ca2+ (mg/l) × 2.497

Mg2+ (mg/l) × 4.116

Fe2+ (mg/l) × 1.792

Zn2+ (mg/l) × 1.531

Mn2+ (mg/l) × 1.822

Al3+ (mg/l) × 5.567

Soap titration Method

All water hardness should not be calculated by the soap titration method such as brines, water hardness over 140 mg/l (required dilution). But it is applicable approximately all water. In this process the determination of water hardness definite by the capacity of soap consuming of the water. The precision and accuracy of determination of water hardness by this process may be variation upon people to people and  the skill and experience of the analyst. Moreover Magnesium hardness is less accurate.

The result is interference by some parameter. Temperature is one of the interfering parameter. It is effects of lather factor and standardization factor. The presences of foam breakers or foaming substances also interfere on the titration result. It is one of the oldest methods for determination of water hardness.

Complexeximetric or EDTA titration method

EDTA titration method for determination of water hardness can also be classified into following method:

Ammonia Buffer procedure

Borate Buffer procedure

Low hardness procedure

Calcium hardness procedure.

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