The Effect of Temperature on Dissolved Oxygen

Planning a (Background Info)

Convert your outline into an introduction on DO using the info you collected previously.

Cite sources of info.

Planning a (Hypothesis)

Write specific hypothesis explaining what should be found. Explain hypothesis or back up by referencing specific sections from background info.

Planning a (Variables)

Independent Variable: Temperature

Dependent Variable: Dissolved Oxygen Concentration

Variables to Control and Methods to Control Them:

a) Air bubbles in the water can be minimized or eliminated by checking for them and refilling the test if necessary. This is because air bubbles can increase the reading of DO when the sample bottle is shaken during mixing.

b) The kit number used should be constant because kit chemicals vary in expiration date and type. The same kit number will be used throughout the experiment.

c)The conditions of the water (atmospheric pressure, salinity, mixing) should stay constant. Mixing and aeration add additional oxygen to the water, affecting results. Salinity (salt content) reduces the amount of oxygen that a water sample can use. Reducing the atmospheric pressure makes it easier for a liquid to lose oxygen. The same water sample should be used throughout. The experiment should be performed during as short a time as possible to reduce the chance these factors will influence the experiment.

d) Oxygen can be lost through heating too quickly. To minimize this, the water shound not be boiled and should be heated slowly. If possible, allow the temperature to stabilize as long as possible.

e) The temperature of the water may cool down during the test because of the time required to mix chemicals and perform the test. This can be minimized by efficient mixing and by using awater bath with thermostat if possible.

f) When pouring or dropping chemicals into the glassware, it is important to be sure that the packets are first opened carefully so as not to spill any of their contents, then to pinch one side into a V for easier pouring. Chemicals that get stuck on the sides may not get mixed into the water. To help this, the dropper should be held the same way each time (during titration) and solid chemicals can be pushed into the liquid by carefully using the stopper.

g) Respiration and photosynthesis performed by organisms in the water sample can create fluctuations in the amount of DO. Therefore, for this lab, use ordinary tap water that has been allowed to sit at the required start temp for at least one-half hour before the experiment.

h) Expired chemicals in the test kits can alter the amount of dissolved oxygen found. When testing, the expiration date of all chemicals used should be similar, and the date should not be passed.

i) Use the same water sample throughout, slowly heating and mixing all at the same time.

j) Use enough quantity of water initially that enough will remain for all planned temperature trials.

* Plastic tub to collect and contain water sample

* Graduated cylinder to measure initial water sample size

* Celsius thermometer (-10 to 100¾C)

* Hot plate or alcohol burner as energy source

* Metal pan to heat the water sample in

* 250 ml beaker to collect water sample from heated pan.

* Insulated gloves or hot pads to protect hands while handling hot objects

* Source of running water for cleaning of glassware

* Distilled or deionized water in squirt bottle to rinse glassware to aboid contamination

* Hach DO test kit (#1469-33)

* Hach DO test kit directions

* DO glass mixing bottle with stopper

* Plastic measuring tube to transfer water to square mixing bottle

* Mixing bottle (23 ml) to hold treated water sample for titrations

* DO reagent 1 powder pillow (manganous sulfate)

* DO reagent 2 powder pillow (lithium hydroxide)

* DO reagent 3 powder pillow (sulfamic acid)

* Bottle of Sodium thiosulfate (0.0109 N) to perform titrations

* Labelled jars with screw top lids to place spent powder pillow packages or liquid wastes in.

* Scissors or fingernail clippers to open powder pillows.

* Safety glasses

1. Put on safety glasses and then obtain Hach DO Test Kit

2. Clean all glassware thoroughly with tap water.

3. Rinse all glassware with distilled water and shake dry over the sink or a plastic tub, being careful not to splash teammates.

4. Fill the metal pan with sample water (tap) and let sit for one-half hour to ensure equilibration of DO in water and allow water to come to room temp.

5. After one-half hour, use beaker to obtain room temperature water sample from metal pan. Pour contents to the top of the glass mixing bottle which is held over the plastic tub to eliminate spills.

6. Drop glass stopper into mixing bottle. Grasp mixing bottle with hand and hold stopper down with index finger. Invert bottle to eliminate excess water from top.

7. Remove stopper from mixing bottle and add reagents #1 & #2 at same time. Carefully pour contents so they don't stick on sides of bottle, or none is lost.

8. Restopper the bottle and check for air bubbles. If large air bubbles are present, remove stopper and replace again until bubbles are removed or minimized.

9. Mix reagents by turning wrist to invert bottle then return to upright position. Repeat for a minute.

10. Set bottle on table and allow precipitate to settle to white line at halfway mark on mixing bottle.

11. Repeat step 9.

12. Repeat step 10.

13. Remove stopper and add powder pillow #3. Air bubbles may be present after this point.

14. Repeat step 9.

15. The solution in the mixing bottle should now be shaded yellow (A deeper yellow means more DO).

16. Pour yellow solution from mixing bottle into measuring tube. Pour contents of measuring tube into titration bottle. Pour additional yellow solution into measuring tube and pour it into the titration bottle.

17. Add sodium thiosulfate, 1 drop at a time to the titration bottle, swirling the contents to aid mixing between drops.

18. Count the number of drops needed to change the yellow liquid to a clear liquid. Confirm the liquid in the titration tube is clear by placing on a white paper.

19. Divide the number of drops needed for titration by two to obtain the DO concentration in mg/L. Example: 21 drops / 2 = 10.5 mg DO/L.

20. Record temperature and DO in table.

21. Dispose of solid and liquid wastes into proper non-toxic containers.

22. Clean all glassware first with tap water, then with distilled water.

23. While performing steps 6-22, slowly heat remaining water in metal pan until it is approximately 10¾ warmer.

24. Repeat steps 5-22 for the second sample and record results.

25. Repeat the experiment so that water samples from 5 different temperatures ranging from room temp to about 40¾ above that have been tested.

26. Wash & return all materials to their appropriate spots.

27. For personal safety, wash your table, then your hands thoroughly with soapy water to remove traces of any chemicals.