CE3L-HW1

CIV ENG 3L03: Homework Assignment #1 (Due: 11:55pm on Feb 5) 1. (4%) (a) Briefly describe what will happen if a large amount of organics is introduced to a natural water system. (b) What will happen if a large amount of nutrients is introduced to a natural water body? 2. (6%) (a) Write the definition of pH. (b) If you have absolutely pure water, what would be the resulting pH? Explain why. Include K w and electroneutrality in your explanation. (c) Describe why pH in rain water is lower than 7. In your answer, make sure to include the following terms in your answer: carbon dioxide, carbonic acid, dissolve (or dissolution). 3. (5%) Sketch the nitrogen cycle. Write a brief description of each of the arrows in your sketch. 4. (10%) (a) Write the definitions of BOD, COD, and NOD. (b) Write the reaction that you expect in COD test tubes. Using the reaction, explain how we estimate the amount of organics in the COD test. (c) What happens if Cl - is present in COD tests? Write the chemical reaction and describe how Cl - affects the COD measurement. (d) What is added in COD test tubes to avoid the Cl - effect? In your explanation, make sure to write the expected chemical reaction(s). 5. (10%) (a) Uric acid (C 5 H 4 N 4 O 3 ) is one of the common organic-nitrogen chemicals found in human urine. Find carbonaceous ThOD for a water containing 10 mg/L of uric acid. (b) Find the total ThOD (including carbonaceous and nitrogenous oxygen demands). (c) Find the nitrogenous ThOD and carbonaceous ThOD. 6. (15%) (a) Describe the steps for BOD tests. (b) Describe how to correct seed bacteria in BOD test. (c) Derive ࠵?࠵? # !(#) ! ! $ = −࠵?࠵? for a BOD test. Start your answer by defining L ( t ) = BOD L – BOD( t ). Assume first-order decay of L during the BOD test (i.e., dL/dt = -kL). (d) BOD test results are given below, plot −࠵?࠵? # !(#) ! ! $ vs. time. You will have to guess a value for BOD L . Assume BOD L is 334 mg-O 2 /L. Find the first order kinetic constant k from the plot. (If you use MS Excel, right click on plotted data points, choose “Add Trendline,” check for “Linear,” set “0” for “Set Interception,” and check for “Display equation” and “Display R-square value.”) Show the resulting plot in your answer. Once k is found, calculate BOD L and compare it with the initial guess. Incubation time (days) 0 1 2 3 4 5 Measured BOD (mg O 2 /L) 0 66 109 147 180 208 (e) If the initial guess of BOD L (334 mg/L) were not given, write a short discussion on how you would find BOD L . 7. (5%) (a) Write the definition of the standard state condition. (b) Write the standard state condition for liquid substances, solids substances, gaseous substances and aqueous substances. 8. (5%) (a) Find the normality of 120 mg/L of Ca 3 (PO 4 ) 2 . (b) Determine the ionic strength of the solution assuming “complete dissolution into Ca 2+ and PO 4 3- .” 9. (5%) (a) Search online and find the hardness of source waters in the following towns: Hamilton, Toronto, and Guelph. (b) Discuss briefly about the found hardness of the water for each of the towns. (c) Determine whether each of the waters is hard or soft according to the WHO criteria. 10. (10%) Calculate the ionic strength for the water samples given below. Before you start calculation, make sure if the electroneutrality is satisfied for the given ionic composition. If it is not, balance the extra charge using either bicarbonate (HCO 3 - ) or proton (H + ). (a) Distilled pure water (pH=7, i.e., [H + ]=10 -7 M; [OH - ]=10 -7 M) (b) River water: [SO 4 2- ]=0.02 mM; [Cl - ]=1.9 mM; [Ca 2+ ]=0.25 mM; [Mg 2+ ]=0.05 mM; [Na + ]=1.1 mM (c) Seawater: [SO 4 2- ]=0.037M; [Cl - ]=0.64 M; [Na + ]=0.57 M; [Mg 2+ ]=0.021 M; [Ca 2+ ]=0.041 M; [K + ]=0.025 M