Determination of Dissolved Oxygen in Water

Determination of Dissolved Oxygen in Water

I. OBJECTIVE/S

To determine the amount of dissolved oxygen in the river water sample MATERIALS • standardized thiosulfate solution • MnSO4 solution • river water sample • Alkali-iodide-azide reagent • starch indicator • concentrated sulfuric acid

APPARATUS • 500-mL Erlenmeyer flask • acid buret • DO bottle • graduated cylinder

III. RESULTS AND DISCUSSION

This experiment was done doing the procedure below:

1. A river sample was collected by dipping the DO bottle below the surface of the river, filling the bottle with water making sure to exclude bubbles while putting the stopper on. 2. 1.0 mL MnSO4 solution was added the mixed by inverting the bottle a few times. It was then followed by 1.0 mL alkali-iodide-azide reagent using different pipets.

3. The stopper was places and the bottle was mixed by inverting it several times. 4. The precipitate was left to settle at the bottom of the bottle. 5. 1.0 mL of concentrated sulfuric acid was added and was mixed again by inverting the bottle several times until the dissolution of the precipitate was completed. 6. The solution was then transferred to a 500-mL Erlenmeyer flask and was immediately titrated with standard thiosulfate solution. 7. As the solution becomes pale yellow, a 2.0 mL starch solution is then added. 8. The solution was then titrated again until colorless. 9. This was performed in two trials and the data was then recorded as shown below.

Trial 1 2

Volume sample used 300.0 mL 300.0 mL

ppm DO 

  



ppm =

)=

   

Corrected Volume Na2C2O3 2.485125 mL 2.58453 mL

)  )    )   

   

 

= 7.766844 mg O2/L



DO =

   

    

= 8.07751776 mg O2/L

   

 

ppm DO (mg O2/L) 7.766844 mg O2/L

8.07751776 mg O2/L

CONCLUSION