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Determination of Hardness of Water Sample

In this determination of hardness of water sample post we have briefly explained about principle, total hardness, temporary hardness, permanent hardness, requirements, determination of hardness of water procedure, results.

Determination of Hardness of Water Sample

Determination of hardness of water defined as those that require a large amount of soap to produce foam, as well as those that cause scale in pipes, heaters, boilers, and other units that raise the temperature of water.

Hard water is suitable for human consumption in the same way as soft water is, but it has an adverse reaction with soap, making it unsuitable for cleaning purposes, necessitating their removal from water. The hardness of the water varies by location. Surface waters are generally softer than ground waters.

Principle

The presence of dissolved calcium and magnesium salts in water causes hardness. It’s unsafe for drinking, swimming, or washing, and it causes boiler scaling. As a result, the amount of hardness-producing chemicals contained in the water sample must be estimated.

The amount of chemicals necessary for water treatment can then be computed once it has been estimated. Complexometric titration is used to calculate hardness. The hardness of water is evaluated by titrating it with a standard solution of the complexing agent ethylene diamine tetra acetic acid (EDTA).

Because EDTA is insoluble, the disodium salt of EDTA is used in this experiment. With a metal ion, EDTA can generate four or six coordination connections.

Total hardness

The presence of bicarbonates, chlorides, and sulphates of calcium and magnesium ions causes total hardness. Eriochrome Black-T (EBT) indicator for EDTA. With the Ca2+/Mg2+ ions present in the hard water, EBT produces a weak EBTCa2+/Mg2+ wine red coloured complex.

In the presence of ammonia buffer, Ca2+/Mg2+ ions preferentially form a stable EDTA-Ca2+/Mg2+ complex with EDTA, leaving the free EBT indicator in solution, which is steel blue in colour.

Temporary hardness

The presence of bicarbonates of calcium and magnesium ions causes temporary hardness. Boiling is an easy way to get rid of it. Temporary hardness-producing chemicals (bicarbonates) precipitate as insoluble carbonates or hydroxides when water is heated. Filtration can be used to remove this precipitate.

Permanent hardness

The presence of calcium and magnesium chlorides and sulphates causes permanent hardness. Boiling will not eliminate this type of hardness. The above-mentioned filtrate contains permanent hardness-producing chemicals, which are measured against EDTA using the EBT indicator.

Requirements

Reagents

1. Water Sample

2. Eriochrome Black-T

3. Ethylene Diamine Tetra Acetic Acid

Materials

1. Burette

2. Pipette

3. Beaker

4. Standard Measuring Flask

Procedure

Permanent Hardness

1. 100 mL of the specified water sample is pipetted into a clean beaker and allowed to boil for 20 minutes.

2. The precipitate generated by the breakdown of transient hardness-producing salts is then filtered off.

3. Using distilled water; make a filtrate up to 100 mL in a standard measuring flask (SMF). Pipette 20 ml of the prepared solution into a conical flask, add 5 ml ammonia buffer, and 2 drops of EBT indicator, and titrate against the EDTA.

4. The change in color from wine red to steel blue marks the conclusion. To obtain a concordant titre value, the titration is repeated.

Total Hardness

1. Pipette 20 mL of the water sample into a clean conical flask. 5 mL ammonia buffer and 2 drops EBT indicator are added to the burette and titrated against EDTA.

2. The change in colour from wine red to steel blue marks the conclusion. To obtain a concordant titre value, the titration is repeated.

Temporary Hardness

1. Temporary hardness-producing chemicals (bicarbonates) precipitate as insoluble carbonates or hydroxides when water is heated. Filtration can be used to remove this precipitate. The temporary hardness is calculated from the total hardness and permanent hardness.

Temporary Hardness = Total Hardness – Permanent Hardness

Further Readings

Reference

Determination of Hardness of Water Sample