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