Two of the most essential parameters for determining water quality would have to be the measurements of dissolved oxygen, and biological oxygen demand. These two measurements are inner-related. Dissolved oxygen is the number of milligrams of oxygen gas dissolved in one liter of water. Biological oxygen demand is the amount of dissolved oxygen lost in a sample of water over a five day period due to organic matter. It is clearly evident that in order to find the biological oxygen demand of a water sample, an initial measurement of the dissolved oxygen would have to be taken.
There are mainly two ways to collect a measurement of dissolved oxygen. A complicated manual way, and by using probes. The manual way is done in seven procedural steps. Step one would be to carefully collect the water sample without splashing and keeping the bottle underwater. This is to prevent air bubbles mixing with the water. Next, add two milliliters of manganese chloride solution, and two milliliters of alkaline iodide solution. After these two solutions are added, add two milliliters of hydrochloric acid. What this did was leave a solution of iodine in an excess of potassium iodide. The dissolved oxygen is now fixed so exposing it to air will not affect the results. Next, take 50 milliliters of the solution and place it in a conical flask .01 m sodium thiosulphate solution should be added. While the sodium thiosulphate solution is being added the conical flask should be shaken until the color becomes pale. When the color is pale three drops of starch solution should be added until this solution clears. The amount of thiosulphate should be recorded. Using these solutions 1 milliliter of .01 M thiosulphate solution is equal to .056 milliliters of oxygen. The final step would be to calculate the concentration of oxygen per liter of water using the following formula: oxygen=(.056y1000)/50 y is the amount of thiosulphate used. The much easi... Continue Reading