Prelaboratory Report Sheetexperiment

Objectives Procedure flow sheet

Waste containment procedure

PRELABORATORY QUESTIONS

1. Explain why the dissolved oxygen content of an environmental sample of water is important.

2. Look up the reported limit values for dissolved oxygen in water so that a system may support aquatic life. What would be the limit value for a system to still be considered aerobic? Anaerobic?

3. Explain what contributes or favors an increased value of dissolved oxygen in water.

4. Which are the main types of pollutants that affect the level of dissolved oxygen in water?

5. In what cases would it be undesirable for dissolved oxygen in water to be present?

6. Establish all the chemical reactions that take place in the modified Winkler Method.

7. Explain what is understood as the ionic force of a solution, what determines it, and how it can be calculated.

8. Explain the concept of salting out and how it affects the solubility of non-electrolytes.

9. What other concept and units besides mg/L is used to express the presence of dissolved oxygen in water? How is this calculated?

10. Using the theoretical approach, calculate the saturation concentration of dissolved oxygen under standard conditions.

11. Using the theoretical approach, explain how you would calculate the concentration of dissolved oxygen at other latitudes and at other temperatures.

Additional Related Projects

• Consider allowing the reduced sample to re-aerate and measure the D.O. level with time in order to determine when the reducing agent is consumed and how fast the saturation level is attained again.

• Consider using in the experiment samples from other natural systems, for example, ocean water.

• An additional experiment can be carried out in which an air-saturated water sample properly seeded with activated sludge is dosed, and the D.O. is measured with time.

• Another experiment would be to add a small amount of a biodegradable organic substrate to an air-saturated water sample seeded with activated sludge and to measure the level of dissolved oxygen vs. time (preferably with the amperometric method). Winkler's method has the disadvantage of being a destructive test, and therefore the amount of mixture or sample would have to be large enough to allow the measurements, yet not interfere too much with the process.

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