Lab:  Winkler Titration to Measure Dissolved Oxygen

Winkler Titration to measure dissolved oxygen

I. Introduction 

A titration is adding a chemical slowly until a specific color change.  These are used to determined concentration of something in a solution.  Today we will use the Winkler Titration to measure the amount of oxygen dissolved in a water sample.   When done correctly a Winkler Titration is more accurate than a digital sensor. 

 II. Safety

·       Wear gloves
·       Wear goggles
·       Report spills to your teacher
 

III.  
·       Water sample
·       La Motte Dissolved Oxygen Kit (store sodium thiosulfate in the refrigerator)

 
IV.  Procedure

1  Fill Water Sampling Bottle
2.  Add 8 drops of Manganous Sulfate
3.  Add 8 drops of Alkaline Potassium Iodide Azide
4.  Cap and mix
5.  Add EITHER 1g scoop of Sulfamic Acid Powder OR 9 Drops of Sulfuric Acid
7.  Cap and mix
8.  Fill Titration tube to the 20mL line
9.  Fill titrator with Sodium Thiosulfate.  Pay attention to amount of Sodium Thiosulfate you add
10 Titrate until sample color is pale yellow
11.  Add 8 drops of Start Indicator, it will turn blue
12  Continue titration with Sodium thiosulfate until Blue color disappears.
13.  Amount of sodium thiosulfate added is equal to ppm of Dissolved Oxygen.

 

V.  Data

What was the dissolved oxygen amount of your sample?

 

VI.  Conclusion

What could cause your measurement to be wrong? 

 

 

 

 

Why do scientists use digital sensors if this method is more accurate?    

© lbranch 2013