3 questions

• answer the questions like these in the file
• e.g.
• Below is the unbalanced chemical reaction for photosynthesis.
• Ammonia (NH₃) is oxidized in the environment to form nitrite (NO₂^–). Nitrite is then oxidized to form nitrate (NO₃^–) in a process called nitrification. The balanced equations are shown below:
• (20pts) A drinking water operator is having trouble disinfecting her treated water, she adds her normal volume of bleach, but bacteria continue to grow. She tests the pH of the water and discovers that the water pH is 8.75. At this pH what is the ratio of Hypochlorous acid to hypochlorite? Why is this a problem for disinfection? (Refer to the slides for equation and Ka values)
• (25pts) Due to anthropogenic emissions, CO2 concentrations in the atmosphere have been increasing. This increase in concentration has resulted in an increased rate of dissolution of CO2 in the oceans. Calculate the concentrations of CO2 in 1960 and 2020 and then calculate the percent increase in CO2 dissolution in the oceans over this time period based off the following figure.

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CO₂ + H₂0+ hv(energy from sunlight}-> C₆H₁₂O₆ + O₂

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• (3pts) Balance the chemical equation by adding coefficients in front of the reactants and products such that the mass in conserved on both sides of the equation.
• (2pts) If the reaction requires an input of energy (sunlight) to proceed, is the reaction endothermic or exothermic?
• (10pts) Calculate the heat of reaction (ΔH) to confirm your answer for part b.
• (5pts) An average tree produces 260lbs of oxygen per year, how many kilograms of carbon dioxide must in take in?
• (10pts) What wavelength (in nanometers) is necessary to drive this reaction?
• BONUS: (2pts) What color is the wavelength in part ‘e’ in the visible spectrum?

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(ΔH for Glucose is -1273kJ/mol).

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(Note: Usually it only takes one photon to dissociate one molecule in simple reactions, but for photosynthesis it takes approximately 10 photons to run this photolysis reaction for one molecule so you should multiply 1.19X10^-4 in your equation by 10, see page 56 if you want to see how this constant was derived)

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2NH₃ + 3O₂-> 2NO₂^– + 2H⁺ + 2H₂0

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2NO₂^– + O₂ -> 2NO₃^–

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• (10pts) Assuming complete oxidation, what is the theoretical oxygen demand to convert 100mg/L of Ammonia to Nitrate? (i.e. How much oxygen is necessary?) Report your answer as g/L O_2.
• (5pts) This conversion process causes the fluid to become acidic, looking at the equations explain why this occurs?
• (10pts) In order for nitrification to occur in a wastewater treatment plant, alkalinity must be added to help maintain pH above 6.8. How much CaCO₃ in g/L would need to be added to the system to offset the impact of the nitrification of 100mg/L of ammonia? (Hint: first find the number of moles of H+ produced)

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Note: At this pH, added CaCO₃ ionizes to calcium and carbonate ions. The carbonate ion can then take up a hydrogen ion as shown in the following reaction.

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CaCO3 + H+-> HCO3- + Ca-

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K_H for CO₂ at 20C = 0.039172 mol/L*atm