Estimation Of Total, Permanent And Temporary Hardness Of Water (EDTA Method)
Aim: To estimate the amount of
total, permanent and temporary hardness in the collected sample of water.
Principle:
Hardness in water is due to the presence of dissolved
salts of calcium and magnesium. It is unfit for drinking,
bathing, washing and it also forms scales in boilers.
Hence it is necessary to estimate the amount of hardness producing substances present in the water sample.
Hardness of water is determined by
titrating with a standard solution of ethylene diamine tetraacetic acid (EDTA)
which is a complexing agent. Since EDTA is insoluble in water, the
disodium salt of EDTA is taken for this experiment.
Total hardness
Total hardness is due to the presence of bicarbonates,
chlorides and sulphates of calcium and magnesium ions. .
Temporary hardness is due to the presence of bicarbonates
of calcium and magnesium ions. It can be easily removed by
boiling. When water is boiled, temporary hardness producing substances (bicarbonates) are precipitated as insoluble carbonates or
hydroxides. This precipitate can be removed by filtration. The permanent
hardness is due to the presence of chlorides and sulphates of calcium and
magnesium ions. This type of hardness cannot be removed by boiling
The total hardness of water is estimated by titrating the
water sample against EDTA using Eriochrome Black-T
(EBT) indicator.
Procedure:
The burette is filled with standard EDTA solution to the
zero level, following usual precautions.
1.
20 Ml of the given
water sample is pipette out into a clean conical flask.
2.
5 ml ammonia buffer and 2 drops of
ebt indicator are added
3.
Titrated against
edta
4.
From the burette.
5.
The end point is
the change of colour from wine red to steel blue.
6. The titration is repeated to get concordant titre value.
Observation table
|
Volume
of water sample (ml) |
Burette
Reading |
Mean
CBR |
|
|
Initial |
Final |
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Calculation
Total hardness = Mean CBR X 1000 / Volume of water sample used
Result :
Total hardness of given water sample is = ---------------ppm
