Test No 6 Dissolved Oxygen water supply practical

Test No. 6 Dissolved Oxygen water supply/ practical Assistant Lect. kasro kakil Hassan 1

Object: To determine the dissolved oxygen content (D. O. ) in a sample of sewage (Azide Modification of lodometric Method or Winkler Method) 2

Introduction: • Adequate dissolved oxygen (D. O) is necessary for the life of fish and other aquatic Organisms. • The D. O test is used in the biochemical oxygen demand (B. O. D) determination. For decomposition of organic maters For control water pollution Methods of measurement 1. Winkler method or Azide Modification oflodemetric method 2. D. O meter 3

Reagents 1. Manganous sulphate solution. Mn. S 04. 4 H 20 2. Alkali- iodide Azide reagent 3. Standard 0. 02 N potassium dichromatic solution. K 2 Cr 207 4. Starch solution 5. Standard 0. 025 N sodium thiosulphate solution: Na 2 S 203. 5 H 20 4

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CALCUATIOCTS: Since 1 ml. of 0. 025 NNa 2 S 2 O 3 titrant is equivalent to 0. 20 mg D. O. each milliliter of. Na 2 S 2 O 3 titrant used is equivalent to 1 mg/L D. O. , if a volume equal to 200 ml. of original sample is titrated. 1 ml of Titrant =1 mg of D. O. Discussion: 1. Effect of Alkali- iodide Azide reagent and starch solution on D. O. test. 2. How we can control the water pollution? 3. Why it is necessary the percent of D. O for organic maters? And Where. 7