Biological oxygen demand (BOD) of water sample analysis Essay Example for Free

Biological oxygen demand (BOD) of water sample synopsis EssayQualitative data Collected sample was very murky The starting line end point colour was of a yellow colour, perhaps non light enough Addition of starch indicator produced a grey-black solution perhaps did not add enough indicator, however this did not pose as a problem There was one occasion where I suspected to have added too much sodium thiosulphate, however the second trial indicated that I did not go past the end point too muchCalculationsTo calculate the dissolved oxygen content (mg/dm or ppm), we must first determine the number of mols of thiosulphate from the mean titrated volume of both samples. In this case, we will use sample A.The Winkler method indicates that the relationship between the amount of oxygen and thiosulphate is a four to one ratio. Therefore, we will divide the number of mols of thiosulphate by four to get the number of mols of oxygen.Then we convert this to milligrams per dm first by multip lying by 20 to arrive with the number of mols present in 1dm (because the pond water sample used was 50cm). Then we multiply that number by 32 (molecular hand of oxygen) to attain the number of grams of oxygen. Then finally, the number is multiplied by 1000 to be converted into milligrams.The biological oxygen demand (BOD) would therefore be the fight between the DO of sample A and sample B.