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How does the temperature of water affect the amount of dissolved oxygen it contains?

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Introduction

THE EFFECTS OF TEMPERATURE ON DISSOLVED OXYGEN: PURPOSE: How does the temperature of water affect the amount of dissolved oxygen it contains? Variable Temperatures (oC): 5, 10, 15, 20, 25, 30, 35. HYPOTHESIS: The higher the temperature of the water, the less dissolved oxygen it will contain. INTRODUCTION: Dissolved oxygen (microscopic bubbles of oxygen gas in aqueous solution, DO) is essential for the healthy functioning of all freshwater ecosystems. If more oxygen is consumed than is produced, DO levels decline and some sensitive animals may move away, weaken and even die. Therefore, DO presence in an ecosystem is a positive sign whereas low DO levels are an indication of severe pollution. Gases are usually more soluble at colder temperatures. For example, oxygen is more soluble in cold water than in hot water. The decrease in oxygen solubility with increased temperature has serious consequences for aquatic life. Power plants that discharge hot water into rivers can kill fish by decreasing the dissolved oxygen concentration. With global industrialization, the conditions of the world have been altered drastically in a short time. Pollutants have been introduced, rivers have been diverted, and forests have been cut down. In general, the higher the DO levels, the more stable the freshwater ecosystem and thus the greater the capacity for this ecosystem to sustain life. Much of the DO in water comes from the atmosphere. Streams with a high kinetic energy and a tumbling water action promote the mixing of atmosphere oxygen, a non-polar compound, with water, a polar compound. ...read more.

Middle

17. Repeat steps 6-16 twice more to obtain an average titre. 18. Repeat steps 6-17 for your other temperatures. 19. Repeat the entire experiment again to make sure your results are accurate. Be sure to note if you have made any changes to the method and reasons why. RESULTS: RESULTS FOR FIRST TITRATION OF THIOSULFATE AGAINST HEAT-TREATED WATER SAMPLE TEMPERATURE (0C) TRIAL 1 (ml) TRIAL 2 (ml) TRIAL 3 (ml) AVG TITRE (ml) AVG dissolved oxygen concentration (mg/L) 5 25.4 25.5 25.3 25.4 25.4 10 24.4 24.3 24.2 24.3 24.3 15 23.2 23.4 23.3 23.3 23.3 20 22.0 22.1 22.2 22.1 22.1 25 21.7 21.5 21.6 21.6 21.6 30 19.2 19.3 19.2 19.2 19.2 35 18.0 17.9 18.1 18.0 18.0 Figure 1: The graph in figure 1 presents the results of the experiments comparing temperature to dissolved oxygen. Each blue diamond represents the average result of three tests performed for each temperature. RESULTS FOR SECOND TITRATION OF THIOSUFATE AGAINST HEAT-TREATED WATER SAMPLE TEMPERATURE (0C) TRIAL 1 (ml) TRIAL 2 (ml) TRIAL 3 (ml) AVG TITRE (ml) AVG dissolved oxygen concentration (mg/L) 5 25.6 25.7 25.5 25.6 25.6 10 24.2 24.1 24.3 24.2 24.2 15 23.1 23.3 23.1 23.2 23.2 20 22.0 22.1 21.9 22.0 22.0 25 21.5 21.4 21.6 21.5 21.5 30 19.0 19.2 19.1 19.1 19.1 35 18.1 18.0 18.2 18.1 18.1 Figure 2: The graph in figure 2 presents the results of the experiments comparing temperature to dissolved oxygen. Each blue diamond represents the average result of three tests performed for each temperature. ...read more.

Conclusion

In my case, I used the same tap, same thermometers and the same bottles of reagents. Also, other than repeating the entire procedure, another method of verifying the dissolved oxygen concentration should be used, like a ?Hach testing kit? or similar apparatus. Further investigations could involve the effects of other variables on dissolved oxygen, such as the presence of pollutants or how certain aquatic plants contribute to the dissolved oxygen level of water. It would be interesting to research whether or not, all tap water is safe for drinking. Factors that you could prove that it is unsafe, could be heavy industrial and environmental pollution. Toxic bacteria, chemicals and heavy metals can penetrate and pollute natural water sources making people sick while exposing them to long term health consequences such as liver damage, cancer and other serious conditions. The world has reached the point where all sources of drinking water, including municipal water systems, wells, lakes, rivers, and even glaciers, contain some level of contamination. Even some brands of bottled water have been found to contain high levels of contaminants in addition to plastics chemical leaching from the bottle. Also, you could follow this experiment by conducting the same procedure and just change a few variables. Such as: ?Does seawater hold as much dissolved oxygen as freshwater at the same temperature?? If the ocean is too far away, make your own saltwater by adding between 30 and 35 g of table salt for each litre of water. Use a water bath, (same one you used for this experiment), for cooling the saltwater sample down without diluting it. ...read more.

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