Question

a) One replicate of the sample is saturated with oxygen at 25 °C for measurement of biochemical oxygen demand, and after five days, the oxygen content is zero. Assuming that the organic matter can be represented as polymeric (CH?O), what mass of carbon has been oxidized in the 1.0 L sample? (2 marks) b) In the river itself, the surface temperature is 10 °C. Using a reliable source for the temperature dependence of the Henry’s law constant of O?, determine the ratio of organic matter than could be oxidized by dissolved oxygen under ambient conditions in the river (i.e. saturated with O? at 10 °C) compared to laboratory conditions. (2 marks) c) A 10 mL sample of river water was titrated with 0.0010 M K?Cr?O? and required 7.0 mL to reach the end point. What is the chemical oxygen demand, in milligrams of O? per liter, of the sample? (2 marks) d) Based on the results of the COD analysis, what is the minimum factor by which you should dilute the original sample to make a more accurate measurement of the BOD in the lab at 25 °C? (1 mark) e) If the subsequent calculation of BOD in the original sample, based on measurements of the diluted sample, is different than the COD from part c), do you expect the BOD to be lower or higher, and how can you explain this discrepancy? (2 marks)

          a) One replicate of the sample is saturated with oxygen at 25 °C for measurement of
biochemical oxygen demand, and after five days, the oxygen content is zero. Assuming
that the organic matter can be represented as polymeric (CH?O), what mass of carbon has
been oxidized in the 1.0 L sample? (2 marks)
b) In the river itself, the surface temperature is 10 °C. Using a reliable source for the
temperature dependence of the Henry’s law constant of O?, determine the ratio of organic
matter than could be oxidized by dissolved oxygen under ambient conditions in the river
(i.e. saturated with O? at 10 °C) compared to laboratory conditions. (2 marks)
c) A 10 mL sample of river water was titrated with 0.0010 M K?Cr?O? and required 7.0 mL
to reach the end point. What is the chemical oxygen demand, in milligrams of O? per
liter, of the sample? (2 marks)
d) Based on the results of the COD analysis, what is the minimum factor by which you
should dilute the original sample to make a more accurate measurement of the BOD in
the lab at 25 °C? (1 mark)
e) If the subsequent calculation of BOD in the original sample, based on measurements of
the diluted sample, is different than the COD from part c), do you expect the BOD to be
lower or higher, and how can you explain this discrepancy? (2 marks)

a) One replicate of the sample is saturated with oxygen at 25 °C for measurement of
biochemical oxygen demand, and after five days, the oxygen content is zero. Assuming
that the organic matter can be represented as polymeric (CH?O), what mass of carbon has
been oxidized in the 1.0 L sample? (2 marks)
b) In the river itself, the surface temperature is 10 °C. Using a reliable source for the
temperature dependence of the Henry’s law constant of O?, determine the ratio of organic
matter than could be oxidized by dissolved oxygen under ambient conditions in the river
(i.e. saturated with O? at 10 °C) compared to laboratory conditions. (2 marks)
c) A 10 mL sample of river water was titrated with 0.0010 M K?Cr?O? and required 7.0 mL
to reach the end point. What is the chemical oxygen demand, in milligrams of O? per
liter, of the sample? (2 marks)
d) Based on the results of the COD analysis, what is the minimum factor by which you
should dilute the original sample to make a more accurate measurement of the BOD in
the lab at 25 °C? (1 mark)
e) If the subsequent calculation of BOD in the original sample, based on measurements of
the diluted sample, is different than the COD from part c), do you expect the BOD to be
lower or higher, and how can you explain this discrepancy? (2 marks)

Added by Michael D.

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