Determination of chlorides in water

Silver ions (Ag+) can precipitate chloride ions (Cl-) as AgCl in a neutral or slightly alkaline solution. In neutral or slightly alkaline solution potassium chromate can indicate the end point of silver nitrate titration of chloride.The determination of chlorides in water can be done by following this method

If silver nitrate is added to a solution containing chloride ions (Cl-) and chromate ions (CrO4–), silver chloride (AgCl) of white colour precipitated first. After all chloride ions are precipitated, silver starts to react with chromate ions to form silver chromate (AgCrO4) of reddish brown colour. This can be taken as the end point and chloride can be quantitatively estimated.

 

 

 

Apparatus used in chloride test in water sample

1. Burette
2. Pipettes
3. Erlenmeyer’s flask 4
4. Measuring cylinder

Reagents:

1. Chloride free distilled water
2. Standard silver nitrate solution (0.0141 N)
3. Potassium chromate indicator
4. Acid or alkali for adjusting pH

Procedure for chloride content determination in water

The chloride test in water sample can be done by following the below steps

1. Take 50ML of sample (V ml) and dilute to 100ML
2. If the sample is highly coloured, add 3ml of aluminium hydroxide and shake well, allow to settle, filter, wash and collect filtrate.
3. Bring the sample pH to 7-8 by adding acid or alkali
4. Add 1ml indicator (Potassium chromate )
5. Titrate the solution against standard silver nitrate solution until a reddish brown precipitate is obtained.
6. Note down the volume (V1 ml)
7. Take 100 mL distilled water in another flask and repeat the procedure from step 3 to 5 and note down the volume of AgNO3 as V2 ml.

The result determined in terms of mg/L of Chloride.

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The video mentioned below shows the how to do chloride test in water sample