General chemistry



University of Houston

Question Description

Please see the attached file. I need you to answer at least 6 out of 9 questions. The answers must be solved manually (not using any software) and all steps and assumptions must be explained Please provide a report in Word file. Thank you.

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1. Calculate the aqueous concentration of Mg+2 in equilibrium with the solid MgCO3 (pKs = 7.46 at I = 0, T = 25C) when the ionic strength = 1.0 M and the temperature equals 25C using the Davies equation incorporated into Table 2.3 (attached). 2. What is the pH of a 10-4 M solution of NaHA assuming that NaHA is the salt of a non-volatile diprotic acid, H2A (pK1 = 6.0, pK2 = 10). Ignore ionic strength effects. Assume T = 25C. 3. Sketch a pC-pH diagram, and use it to find approximate pH of the following solution at equilibrium. Show all work for full credit. Recipe: [NH4Cl]T = 10-3 [NaOH] = 10-3, PNH3 = 10-6 atm Species: H2O, H+, OH-, Na+, Cl-, NH4+, NH3(aq), NH3(g) Reactions: NH4+ = NH3(aq) + H+ pKa = 9.2 NH3(g) = NH3(aq) pKH = -1.8 1 4. Planet Thethys has a nitrogen and hydrogen sulfide atmosphere. Thethysian aquatic chemists have defined the alkalinity expression with respect to the H2S equivalence point. Assuming only sulfide system contributes to alkalinity, what is the pH of a Thethysian lake having an alkalinity of 10-3 M, PH2S = 10-3 atm. 5. The upper layer of a thermally stratified lake (epilimnion) has a pH = 7.0, an alkalinity of 10-3M and a boundary layer thickness (Z) of 0.003 cm. Assuming only the carbonate system contributes to the alkalinity and ignoring any chemical enhancement factor associated with the chemical reaction of H2CO3, calculate the flux of CO2(g) across the surface of a lake (T = 25˚C) in equilibrium with a PCO2 of 10-3.5 atm. The molecular diffusion coefficient for CO2 is 5 x 10-5 cm2s-1 and KH for CO2 is 10-1.5 M/atm at 25 ˚C. 6. Calculate the pH of a water open to the atmosphere where CT and alkalinity are approximately equal at 1.6 x 10-3 eq/L assuming carbonate to be the only weak acid. Show all work and list all assumptions. Solve algebraically or use pC-pH graph. 7. Calculate the pH of a natural water with an alkalinity of 1 x 10-4 eq L-1 at equilibrium with an atmosphere having a PCO2 = 10-3.5 atm. Show all work for full credit. Reactions H2O = H+ + OH- pKw = 14 CO2(g) + H2O = H2CO3* pKH = 1.5 H2CO3 = H+ + HCO3- pK1 = 6.3 HCO3- = H+ + CO3-2 pK2 = 10.3 8. Calculate the alkalinity of a solution having the following recipe. Assume only the carbonate system is important. PCO2 = 10-3.5, pH = 7.3. Show all work for full credit. 9. What is the pH of a solution having the following recipe? Assume open system, PCO2 = 10-3.5 atm. Show all work for full credit. Assume HCl is a strong acid. Recipe: [Na2CO3] = 10-3, [HCl] = 102 Potentially useful information For CO2: PCO2 = 10–3.5 atm, KH = 10-1.5 moles/L atm at 25˚C (CO2(g) + H20 = H2CO3*) at 25˚C For H2CO3: pKa1 = 6.3 and pKa2 = 10.3 at 25˚C For H2S, K = 0.1 moles/L atm at 25˚C (H2S (g) = H2S (aq)) For H2S, pKa1 = 7.0 and pKa2 = 14 at 25˚C For H3PO4, pKa1 = 2.1, pKa2 = 7.3, pKa3 = 12.3 at 25˚C Assume that all salts, acids and bases not specifically listed completely dissociate. R = 1.987 cal/mole deg = 8.314 J/mole deg = 0.08206 L atm/mol deg Van’t hoff equation: ln [KT/K T0] = - ∆H/R[1/T – 1/T0] Jg = 10-3(D/Z)(Cgsat –Cg) Where Jg is the flux of the gas per unt area (mol cm-2 s-1), D is the molecular diffusion coefficient of the gas (cm2 s-1), Cgsat is the concentration (mol L-1) of the gas in equilibrium with the given partial pressure Pg, Cg is the concentration of the gas in the bulk aqueous phase and Z is the average depth of the water laminar boundary layer through which the diffusion is taking place (cm) 3 4 5 ...
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