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Dissolved Oxygen in water

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Introduction

Chemistry Coursework BY WASIM KHOURI Y12 SL CHEMISTRY Contents Design 3 Data Collection and Processing 6 Conclusion and Evaluation 9 Design Research Question: How does the dissolved oxygen content vary at different stages of the sewage treatment plant in Istra? Hypothesis: Dissolved oxygen in water is very important for many plants and animals so that they can undergo aerobic respiration. At a pressure of one atm and a temperature of 20 �C the maximum solubility in water is only about (9 mg l-1) 1and therefore, I believe that the dissolved oxygen in the water will not exceed 9 mg l-1 at all stages of the water treatment. Before I predict what the results will be like, it is vital that you know from what stages of the sewage treatment did I take water samples. The samples are taken from four sections that will be named raw sewage-this is where the water is still very dirty and hasn't yet been processed at all, air and bacteria tank- here bacteria and air (mainly oxygen) are added to the water, chlorination tank and oxygenation tank. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis2. As a result, I believe that raw sewage will have very low dissolved oxygen content due to the fact that it may have a lot of bacteria that will undergo aerobic respiration and that will use oxygen when they decompose. The water taken from the air and bacteria tank is likely to have much higher dissolved oxygen content because air (oxygen) ...read more.

Middle

13. Step 9: Add 1 drop of Starch Indicator through the cap port and mix by carefully swirling the vessel in tight circles. The solution will turn a violet to blue color. 14. Step 10: Push and twist pipette tip onto tapered end of syringe ensuring an air tight-fit. Take the titration syringe and push the plunger completely into the syringe. Insert tip into HI 3810-0 Titrant Solution and pull the plunger out until the lower edge of the plunger seal is on the 0 mL mark of the syringe. 15. Step 11: Place the syringe tip into the cap port of the plastic vessel and slowly add the titration solution dropwise, swirling to mix after each drop. Continue adding titration solution until the solution in the plastic vessel changes from blue to colorless. 16. Step 12: Read off the milliliters of titration solution from the syringe scale and multiply by 10 to obtain mg/L oxygen. 17. Take the other samples and repeat Step 1 to Step 12. 18. When you finish make sure that you dispose of the water into somewhere safe i.e. the toilet. Don't spill it on the ground or grass or back into the sewage as this is regarded as non-scientific action. 19. Finally, and most importantly when you packed away all your equipment wash your hands very carefully with soap. Method of Collecting Data: We talked about how to carry out the experiment but we didn't really say how to collect the data. 1. Take one sample from the raw sewage tank because it is hard to get more due to the fact that the area is very small. ...read more.

Conclusion

This is a real weakness because the temperature of the water affects the dissolved oxygen a lot: as the temperature increases the solubility of the water decrease. Furthermore, our second biggest problem was that we couldn't control time. Ideally, the experiment would be done by taking a sample, immediately finding its dissolved oxygen content and then taking another sample and doing the same. However, because of lack of apparatus and more importantly time, I had to take half the samples, leave the plant find the dissolved oxygen content of those and then get the other half and do the same thing. Consequently, the dissolved oxygen content might have changed while the samples were just waiting to be processed. Improvements: In order to realistically improve this experiment we would have to use a dissolved oxygen probe that can obtain the dissolved oxygen content immediately. That way we can get a sample and immediately find its dissolved oxygen content without exposing it to air and hence not allowing more oxygen to dissolve. Similarly, we can take readings from different sections of each tank including depth samples in order to get more accurate and viable results. Another interesting aspect for further investigation would be the Biological Oxygen Demand (BOD) which is also a measure of the dissolved oxygen required to decompose the organic matter in water biologically. This would have to be measured over a period of 5 days and a fixed temperature of 20�C. 1 - IB study guide (page. 135)- Chemistry for the IB Diploma Standard and Higher by Geoffrey Neuss (Oxford) 2 - http://www.state.ky.us/nrepc/water/wcpdo.htm 3 http://www.hannainst.com/manuals/manHI_3810.pdf ?? ?? ?? ?? Wasim Khouri Chemistry SL ...read more.

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