Estimation of Dissolved oxygen from water sample

 Aim:  To Estimation of Dissolved oxygen from water sample

All living organisms depend upon oxygen to maintain the metabolic processes that produce energy for growth and reproduction . Dissolved oxygen is important in precipitation and dissolution of inorganic substances in water Need To assess quality of raw water.  To check on pollution ¾ Determination of biological changes by aerobic or anaerobic organisms . D.O. is the basis of BOD test to evaluate pollution potential of wastes.  

Dissolved Oxygen is the amount of gaseous oxygen (O2) present in the water in its dissolved state. DO is the most important indicator of the health of a water body and its capacity to support a balanced aquatic ecosystem of plants and animals.  A higher dissolved oxygen level indicates a better water quality. If dissolved oxygen levels are too low, some fish and other organisms may not be able to survive.

The Winkler Method is a technique used to measure dissolved oxygen in freshwater systems. Dissolved oxygen is used as an indicator of the health of a water body, where higher dissolved oxygen concentrations are correlated with high productivity and little pollution. This test is performed on-site, as delays between sample collection and testing may result in an alteration in oxygen content.

Reagents

1.      2ml Manganese sulfate

2.      2ml alkali-iodide-azide

3.      2ml concentrated sulfuric acid

4.      2ml starch solution

5.      Sodium thiosulfate

Procedure

1.      Collect sample in BOD bottle

2.      2 ml mnso4 (Wrinklers- A Soln. ) + 2 ml Alkali iodide-azide (Wrinklers –B Soln) in close stopper bottle

•     Mix well + allow the ppt to settle
•    Add 2 ml concentrated H2SO4 + mix well till ppt dissolves
•    Take 2 to 3 ml (Correspond to sample ml) sample in a conical flask
•    Titrate against Sodium thiosulphate (0.025 N)
•     End point is blue to colourless

  Observation table

Volume of water sample (ml)	Burette Reading (Sodium thiosulphate)		Mean CBR
	Initial	Final

Calculation :  1 ml of 0.025N Na2S2O3 = 0.2 mg of O2

Normality of Sodium thiosulphate  (0.25 N)

Eq. Wt. of oxygen Volume of sample 1000

D.O. in mg/l = 

 

Result :

The  D.O. from given waer sample is ----------------  mg/l