Environmental Biotechology

Experiment 1

Introduction:

The potable water is chlorinated to make the water free from microorganisms. However, sometimes the concentration of chloride ions in water is increased than what is normally required. Apart from this water also receives chlorides ions from multifarious sources.The chloride ions (Cl^-) can be estimated by titrating with silver nitrate solution.

Materials required:

1. Water sample

2. Conical flask

3. Pipette

4. Titration assembly

5. Silver nitrate (AgNO3) solution (0.025N)

6. (dissolve 3.4 g dried AgNO, in distilled water and dilute to make 1 litre. Store in coloured bottle)

7. Potassium dichromate solution (5%)

8. (dissolve 5 g of K,Cr,0, in 100 ml of distilled water)

Procedure:

1. Take 50 ml of sample in a conical flask and add 2 ml of K2C2O7 solution. Pour 0.025N AgNO3 solution into burette set with titration assembly.

2. Titrate the water sample with AgNO3 solution until reddish tinge appears.

3. Note the end point (AgNO3 reacts with CI^- ions and forms very slightly soluble white precipitate of AgCl2 (silver chloride). Free silver ions (Ag+ +) react with chromate ions (Cr2O7) to form silver chromate of reddish brown colour).

Result:

Calculate the amount of chloride ions in water sample as below: Chloride (mg/litre) = VolumeofAgNO3solutionx1000x355

Volume of water sample used