Chem 1008 prelim 2 - 1 2 3 4 5 6 7 8 These are practice problems for the second prelim exam. These problems will not be collected

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Unformatted text preview: 1. 2. 3. 4. 5. 6. 7. 8. These are practice problems for the second prelim exam. These problems will not be collected or graded. They are only for use to prepare for the exam. A sample of ammonium iodide is heated to 400 °C in a 2.0 L flask. The reaction below occurs, and at equilibrium the pressure in the flask is 705 mmHg. NH4I (s) NH3 (g) + HI (g) (a) Calculate Kp. (b) Calculate Kc. (c) How many moles of NH3 are present at equilibrium? Calculate the pH and percent ionization at equilibrium for a 0.100 M HClO2 solution. The Ka for HClO2 is 0.011. The pH of an unknown acid solution is 2.82. The initial concentration of unknown acid is 0.13M. What is the equilibrium constant of this acid? Calculate the pH at equilibrium of a 2.07x10 ­7 M solution of HI in pure water at 25 °C. Determine the Kc value for the reaction: 2N2O(g) + 3O2(g) 2N2O4(g) Given the following equilibrium constant values: (a) N2(g) + ½ O2(g) N2O(g) Kc=2.7x10 ­18 (b) N2O4(g) 2NO2(g) Kc=4.6x10 ­3 (c) O2(g) + ½ N2(g) NO2(g) Kc=4.1x10 ­9 Calculate the pH of a solution resulting from the combination of 100.0 mL of 0.36 M solution of the weak base, hydroxylamine (NH2OH, Kb = 1.10x10 ­8), and 50.0 mL of a 0.26 M solution of HCl at 25 °C. Combining 150 mL of a 0.25 M formic acid (HCO2H, Ka = 1.8x10 ­4) solution with 75.0 mL of a NaOH solution generates a buffer with a pH of 3.56. What is the concentration of the NaOH solution? 2.6 grams of NaCHO2 are dissolved in pure water to make 500.0 mL of solution. What is the pH of this solution? (HCO2H, Ka = 1.8x10 ­4) 9. Indicate the effect (shift right, shift left, no effect) of each of the changes below to the following reaction at equilibrium: C(s) + 2H2(g) CH4(g) ΔH=  ­25kJ/mole (a) Add more C to the reaction mixture (b) Add H2 to the reaction mixture (c) Remove H2 from the reaction mixture (d) Add krypton (Kr) gas to the reaction mixture (e) Add a catalyst to the reaction mixture (f) Raising the temperature of the reaction mixture (g) Reducing the volume of the container 10. A 25.00 mL solution of 0.115 M RbOH is titrated with 0.100 M HCl solution. (a) Calculate the initial pH (before the titration begins) (b) Determine the volume of titrant needed to reach the equivalence point (c) Calculate the pH at the equivalence point (d) Calculate the pH after 25.00 mL of titrant has been added (e) Calculate the pH after 35.00 mL of HCl titrant has been added (f) Using the textbook, page 722, and your results, which indication would you use for this titration. 11. A 122.96 gram sample of Na3PO4 is dissolved in pure water to make 750.0 mL of solution. For H3PO4: Ka1=7.1x10 ­3, Ka2=6.3x10 ­8, Ka3=4.2x10 ­13. (a) Give the material balance equation for all phosphorous containing species. (b) Give the material balance for all sodium containing species (c) Give the electroneutrality equation for this solution (d) Write the four equilibrium constant expressions involved in this solution. (e) Rearrange each Ka to give concentrations of each acid in terms of [H3O+] and [PO43 ­ 12. Calculate the pH of a 4.30x10 ­7 M LiOH aqueous solution at 25°C. 13. Use Lewis structures and arrows to show the autoionization of water. 14. A 0.25 ­mole sample of a weak acid with an unknown pKa was combined with 20.0 mL of 3.00 M KOH and the resulting solution was diluted to 1.500 L. The measured pH of the solution was 3.85. What is the pKa of the weak acid? 15. A 0.552 ­gram sample of ascorbic acid (vitamin C) was dissolved in water to a total volume of 20.0 mL and titrated with 0.1103 M KOH, and the equivalence point occurred at 28.42 mL. The pH of the solution at 10.0 mL of added base was 3.72. From this data determine the molar mass and Ka of vitamin C. 16. The Kb of hydroxylamine, NH2OH, is 1.10x10 ­8. A buffer solution is prepared by mixing 100.0 mL of a 0.36 M hydroxylamine solution with 50.0 mL of a 0.26 M HCl solution. Find the pH of the resulting solution at 25°C. 17. For the synthesis of ammonia (NH3) at 500 °C, the equilibrium constant is 0.060. Predict the direction in which the system will shift to reach equilibrium if the current concentration for each species is: [NH3]=1.0x10 ­4 M, [N2]=0.050 M, [H2]=0.010 M. 18. A 50.00 ­mL solution of a weak acid HA (Ka=5.00x10 ­10) in water has a pH=5.650. Calculate the amount of water that must be added to reach a pH value of 6.650 at 25°C. 19. Consider the titration of 25.0 mL of 0.100 M lactic acid (HC3H5O3, pKa=3.86) with 0.100 M KOH. (a) What is the initial pH before the titration starts? (b) What volume of KOH that must be added to reach the equivalence point? (c) What is the pH at the equivalence point? (d) What is the pH after 20.00 mL of KOH has been added? (e) What is the pH after 28.0 mL of KOH has been added? 20. A 25.0 ­mL sample of 0.100 M NH3 (Kb=1.8x10 ­5) is titrated with 0.100 M HCl solution. (a) What is the initial pH before the titration starts? (b) What volume of HCl that must be added to reach the equivalence point? (c) What is the pH at the equivalence point? (d) What is the pH after 8.00 mL of HCl has been added? (e) What is the pH after 30.00 mL of HCl has been added? ...
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This note was uploaded on 04/29/2011 for the course CHEM 2080 taught by Professor Davis,f during the Spring '07 term at Cornell University (Engineering School).

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