Tag: water hardness

Determination of hardness of water by EDTA method

Tasrik 8 Comments

Determination of hardness of water by EDTA method is one of the three main methods for determination of hardness of water. EDTA means Ethylenediaminetetraacetic acid. This EDTA reagent can be forming edta-metal complexes by the reaction with metal ions except for alkali metal ions. This reagent can forms a stable complex with the alkaline earth metal like calcium ion and magnesium ion in alkaline condition pH above 9.0. Therefore the total hardness of water can be determination by edta titration method.

In this method buffer solution is used for attain suitable condition i.e pH level above 9 for the titration. Buffer solution preserve pH at a balanced position. In aqueous solution edta exist as H2Y2- form. Hence edta react with alkaline earth metals as 1:1. As a result for every mole of alkaline earth metal ion in water sample, one mole of EDTA will be consumed during titration.

Reaction: H2Y2- + M2+ → MY2- + 2H+

During titration Eriochrome Black T is used as indicator. The indicator is red in color when it is forms complexes with the metal ions and blue in color when it is free.

Reaction: MIn– + H2Y2- → HIn2- + MY2- + H+

Determination of hardness of water by EDTA method is father classified into four methods.
Determination of hardness of water-1971

  • Ammonia Buffer procedure
  • Borate Buffer procedure
  • Low hardness procedure
  • Calcium hardness procedure.

Ammonia Buffer procedure: This type determination of hardness of water by EDTA method is especially preferred for those water, where is unfamiliar composition, sewage water, alkalinity or acidity high and for industrial waste water. This method can also be used for normal water. A high capability buffer solution is used to conquer buffering substance in the sample. It has mainly three disadvantages;

  • Utilize of ammonia buffer solution may perhaps not be acceptable if Nessler ammonia determination are being carried out in the same room.
  • If the water sample contains high in calcium ion and bicarbonate ion, it is a affinity for calcium carbonate to be precipitated.
  • The existence of magnesium in the titrant.

Borate Buffer procedure: Borate buffer method is a simpler among the determination of hardness of water by EDTA method. This method is to overcome the limitation of ammonia buffer method. This method does not liberate any ammonia; somewhat calcium carbonate precipitated but not totally holds back. It is not suitable for those water; which is unfamiliar water sample, contains acidity or high alkalinity, industrial waste and sewage.

Low hardness procedure: This is another type of determination of hardness of water by EDTA method. This method is used for waters of low hardness less than 5 mg/l and also for ionexchange effluent or other conditioning water.


Calcium hardness procedure: This method is used for determination of calcium hardness, but it is not standard accurate method for calcium.

Determination of Water Hardness

Tasrik 2 Comments

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.