Determination Of the total hardness of water.

Determination Of the total hardness of water


Theory: Water Hardness is a traditional measure of the capacity of water to precipitate soap.

In fresh water, the principal hardness causing ions are calcium & magnesium with precipitate soap.
Total hardness is defined as the sum of the calcium & magnesium concentration, both expressed as CaCO3, in mg/l.

Soft Water              0-75mg/l
Medium Water       75-150mg/l
Hard water             150-300mg/l
Very Hard Water   >300mg/l


Principle: EDTA (Ethiline Diemine Tetra Acitate) & sodium salts forms a geletanious soluble complex when added to a solution of a certain metallic cations.
If a some amount of Chrome Black T is added to sample at pH=10, it will give wine red colour with magnesium & calcium salts.
If EDTA  is added, it reacts with calcium & magnesium from dry complex.
The solution will turn from wine red to blue colour.
This is the end point of the titrarion.

Apparatus Required: Burette, Burette Stand, Pipette, Two Conical Flasks, Measuring Cylinder, Standard N/50 EDTA Solution, Eriochrome Black T indicator, Ammonia Buffer( to raise pH of water to about 10)

Procedure:

1. Take 100ml of water sample in a conical flask.
2. Add 1ml of Ammonia buffer to flask.
3. Add 6 drops of Eriochrome Black T indicator to flask. Wine Red colour will be developed.
4. Titrate it with standard EDTA solution till the colour changes from wine red to blue.

Calculations:


Hardness in mg/l as CaCO3=
(ml of EDTA used x N/50 x 50 x 1000)/ ml of water sample


Result: The hardness of the given water sample is found to be _____mg/l.

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2 comments

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August 10, 2018 at 12:36 AM delete

Products listed on our website are either in stock or can be resynthesized within a reasonable time frame. Eriochrome Black T

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November 1, 2023 at 5:45 PM delete

The experiment uses EDTA to determine water hardness as CaCO3, with color change from wine red to blue as the endpoint. visit for tanker lorry water supply in chennai anna nagar
lorry water supply in chennai anna nagar

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