Remember: You can use notes on both sides of one sheet of paper.

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1 Chem 5 Fall 2001 Final Exam 150 points total Name: Remember: You can use notes on both sides of one sheet of paper. A periodic table and sheet of equations is provided. Turn in the note sheet with your exam. Significant figures will be included in points for each numerical problem. Point values for each question appear in parentheses in the margins My signature below means that I agree to uphold the Honor Principle in taking this exam. Signature: Please wait to start your exam until everyone is seated and the instructor tells you to begin. There are useful tables and equations on the first pages of the exam. Good Luck!

2 Useful Equations, Constants, and Conversion Factor R = J mol 1 K 1 = L atm mol 1 K 1 N a = x 1023 e = x C ε o = x C2 J 1 m 1 g = 9.81 m s 1 Pa = 1 kg m 1 s 2 1 atm = x 105 Pa 1 atm = 760 torr k = x J K 1 F = 96, C/mol V = J/C T (K) = T ( C) PV = nrt P a = X a P tot KE for 1 mole of gas = 3 RT u rms = µ (D) = H = E p V = Q p E = q + w 3RT M P = 1 N mu2 f (u) = 4π m 2πk T 3 2 u 2 exp mu2 2k T R (Å) Å D 1 δ H = C tot T S = dq rev /T S = n c p ln T f /T i S vap = H vap /T vap S fus = H fus /T fus G = H T S G = Gº + RT ln Q Gº = RT ln K S = k ln Ω K c = K p (RT) n ph = log [H 3 O + ] pk a = log K a K w = = [OH ][H 3 O + ] ph = pk a log [HA]/ [A ] G = n F ε Gº = n F εº εº = εº cathode εº anode ε = εº RT/ nf ln Q ε = εº V/ n log Q ln K = Gº /RT = nf εº /RT

3 H 2 O (l) Thermodyanamic Data Hº f Sº C p J/mol K = J/g K C (graphite) J/mol K C (diamond) kj/mol J/mol K Standard Reduction Potentials at 25ºC

4 1. Choose FOUR of the following 6-point questions to answer. (24 total, 6 each) A. What is the ph of a saturated solution of Al(OH) 3? The K sp of Al(OH) 3 is at 298 K. B. Write the Lewis structures of the following ions or compounds, including all important resonance forms and labeling each atom with its formal charge. CO 3 2 NH 4 + SF 4

5 1. CONTINUED.Choose FOUR of the following 6-point questions to answer. (24 total) C. A M solution of a monoprotic weak acid has a ph of What is the pka of the acid and its possible identity? D kg of lead (specific heat=0.128 J/g K) at 100.0ºC is added to an insulated container filled with water at 28.5ºC. After the lead and water reach thermal equilibrium, the final temperature is 35.2ºC. What is the mass of water present in the container, assuming there is no heat lost to the surroundings or the container.

6 1. CONTINUED.Choose FOUR of the following 6-point questions to answer. (24 total) E. Pure nitrosyl chloride gas, NOCl, was heated to 240ºC in a 1.00 L container and the following equilibrium was established. 2 NOCl (g) 2 NO (g) + Cl 2 (g) At equilibrium, the total pressure was 1.00 atm and the partial pressure of NOCl was 0.64 atm. Calculate the partial pressures of NO and Cl 2 and the value of K p at this temperature. P NO = P Cl2 = K p = F. Consider the conversion C (graphite) C (diamond) Using the data on the front of the exam, calculate the following thermodynamic properties: Hº = Sº = Gº = Is the reaction spontaneous at 298K? Can the spontaneity be changed? If so, at what temperature with the spontaneity change?

7 2. Tarnish on silver consists primarily of silver sulfide, Ag 2 S(s). It can be reduced to silver metal with the following half-reaction: Ag 2 S (s) + 2 e 2 Ag (s) + S 2(aq) Eº = V A household tips book suggests removing tarnish by rubbing tarnished silver with a paste of baking soda and water, on a piece of aluminum foil. Theoretically, this process should convert the tarnish to shiny silver metal. (3) Write an oxidation half reaction that occurs when silver is polished in this way and the Eº, FOR THE OXIDATION REACTION, AS WRITTEN. (3) Write a balanced net reaction and calculate the Eº for the overall reaction. (4) Calculate Gº and K for the reaction, at standard state conditions.

8 2. CONTINUED. Prof. Hair does not want to spend time rubbing silverware with aluminum foil and prefers to set up an electrochemical cell to reduce the Ag 2 S on her spoons to Ag(s). Use the oxidation half-reaction and net reaction from the previous page to make a galvanic cell. Describe the cell using standard notation, below and label the parts of the cell on the drawing below. Note that the Ag 2 S is a solid that is reduced to silver metal, not dissolved ions in solution. Your cell notation should show this. (2) Cell in standard notation: (8) Sketch the cell and label the cathode, anode, and salt bridge. Next to each electrode write the half-reaction taking place and the material that makes up the electrode. Show the direction of ion flow in the salt bridge. Show the direction of electron flow in an external circuit. Voltmeter

9 3. Multiple Choice: There may be more than one correct answer. Questions with NO (40 ) choice circled will receive zero points. (4) Heavy water consists of D 2 O, where D stands for the isotope deuterium, 2H. For pure heavy water at 25ºC, the equilibrium constant for the self ionization of D 2 O is If pd is defined analogously to ph and pod analogously to poh, which of the following statements are true? A. pd + pod = 14 B. A solution in D 2 O with a pd of 7 is acidic. C. Pure D 2 O has a pd of 7.43 D. The concentration of D 3 O+ in pure D 2 O is less than the concentration of H 3 O+ in pure water. (4) Prof. Hair continued to investigate the galvanic cell used in the Tutti Fruity Clock by placing its two electrodes in 1.0 M solutions of various metal ion salts. She mixed up the beakers containing Zn+2, Cu+2, and Fe+2 salts, but measured a voltage of V when she placed the two electrodes in two different solutions. What cell has she most likely created? A. Zn Zn+2 Fe+2 Fe B. Zn Zn+2 Cu+2 Cu C. Cu Cu+2 Fe+2 Fe D. Fe Fe+2 Cu+2 Cu (4) When is it possible for a substance to have a standard entropy of zero? A. at T = 0 K. B. at equilibrium. C. when it is an element in its standard state. D. when it is formed spontaneously from elements at standard states. (4) An indicator, HIn, changes from yellow to blue as the ph changes from 4 to 5.5. Which of the following statements would be true of HIn? A. HIn has a pka between 4 and 5.5. B. If a solution of HIn were titrated, it would have an equivalence point between ph 4 and 5.5. C. HIn is blue and In is yellow. D. HIn is yellow and In is blue.

10 (4) For the reaction in which solid carbon dioxide (dry ice) sublimes to become gaseous carbon dioxide, CO 2 (s) CO 2 (g), which of the following is true for the reaction as written? A. The reaction is exothermic and entropy is increasing. B. The reaction is exothermic and entropy is decreasing. C. The reaction is endothermic and entropy is increasing. D. The reaction is endothermic and entropy is decreasing. (4) If you have available solution of HCl, NaOH, CH 3 COOH, and NaCH 3 COOH, which pairs could you use to make a buffer solution? A. HCl and CH 3 COOH B. NaOH and CH 3 COOH C. NaOH and NaCH 3 COO D. HCl and NaCH 3 COO (4) The molar enthalpy of formation of CO 2 (g) is equal to A. The enthalpy change for complete oxidation of 1 mole of graphite by oxygen. B. The molar enthalpy of combustion of C (graphite) C. The sum of the molar enthalpies of formation and combustion of CO (g) D. Two times the bond enthalpy of a C=O bond. (4) A balloon is filled with 0.2 moles of H 2 gas and 0.1 moles of O 2 gas and ignited. How many moles of H 2 O will form? A moles B. 0.1 moles C. 0.2 moles D. 0.3 moles (4) Which of the following is true at equilibrium? A. The change in free energy with respect to extent of reaction is zero. B. The concentration of products and reactants are equal. C. The concentration of products and reactants are constant. D. The rates of forward and reverse reactions are equal. (4) Using formal charges to evaluate Lewis structures for the nitrate ion, NO 3, what would you predict the bond order of the N-O bond to be? A. 1.5 B C. 2 D. 1.67

11 4. Consider a 2.00 M solution of nitrous acid, HNO 2. (4) Write the acid dissociation reaction and label the acid and conjugate base. (4) Calculate the ph of the solution. (6) ml of the above solution is combined with ml of 1.3 M NaOH solution. What is the ph of the new solution?

12 4. Continued.. (4) How much ADDITIONAL base would you need to add to the solution to reach the equivalence point? (4) What is the ph at the equivalence point?

13 5. Ion exchange chromatography can be used to determine the K sp of an ionic solid using the experiment described below: A saturated solution of PbI 2 is made and ml of the solution is pipetted onto a large cation exchange column. On the column, the cations are exchanged for H 3 O+ ions, which are collected in the effluent. The column is carefully rinsed and the entire effluent is titrated with M NaOH solution ml of NaOH solution is required to titrate the effluent to a phenolpthalein endpoint. Recall that cation exhange resin exchanges one mole of H 3 O+ ions for every equivalent of cation charge. Before calculating the K sp of PbI 2, answer the following questions: (4) Write a balanced net ionic equation for the reaction of cations in the saturated solution with sulfonic acid groups, R-SO 3 H of the ion exchange resin. (4) Write the chemical equation for the solubility equilibrium of PbI 2 and the expression for its K sp. (8) What is the K sp of PbI 2, according to the above experiment?

14 6. (28) Consider each of the situations on the left and match it with a concept, Law, or name on the right. Write the appropriate letter or letters in the blank line, on the far left. THERE MAY BE MORE THAN ONE CORRECT LETTER! A 3.16 g sample of an unknown gas occupies a volume of 863 ml at 25ºC and 1.00 atm. It s molar mass can be determined using which letter(s)? Calcium carbonate is more soluble in a buffer at ph=4 than in pure water. This is due to which letter(s)? A. Prof. Hair B. Law of Conservation of Mass C. Law of Multiple Proportions D. Law of Combining Volumes XeF 4 violates this letter(s). When benzoic acid is titrated to its equivalence point with strong base, the ph of the resulting solution is basic. Which letter(s) explain(s) why it isn t neutral? When graphite is burned to yield CO 2, 394 kj of energy are released per mole of C atoms burned. When Buckminsterfullerene, C 60, is burned to yield CO 2 approximately 435 kj of energy is released per mole of carbon atoms burned. To decide if the C 60 -to-graphite conversion is exothermic or endothermic, which letter(s) would you use? To calculate the K sp of an insoluble salt from its solubility in moles/l, which letter(s) would you use? In a mixture of He and Ar gases at room temperature, the He atoms are on average travelling about 3 times faster than the Ar atoms, according to which letter(s)? A 0.17 g of hydrogen (at 1 atm at 298 K) is ignited and reacts with 1.31 g oxygen to produce 1.48 g water. Which letter(s) is(are) illustrated? The volume of a sample of gas (at constant pressure and number of moles) is measured are a series of temperatures. Extrapolation of the observed relationship can be used to determine the absolute zero of temperature. MORE ON NEXT PAGE! E. Law of Definite Proportions F. Avogadro s Hypothesis G. The Octet Rule H. Charles Law I. Boyle s Law J. Ideal Gas Law K. Dalton s Law of Partial Pressures L. Kinetic Molecular Theory M. Maxwell-Boltzmann Distribution N. First Law of Thermodynamics O. Hess s Law P. Second Law of Thermodynamics Q. Third Law of Thermodynamics R. Law of Mass Action S. LeChatelier s Principle T. Hydrolysis Reaction U. Common Ion Effect

15 For a particular process, you predict that the entropy of the system will increase and the entropy of the surroundings will increase. Which letter(s) tell(s) you whether or not the process will happen spontaneously? Nitrogen froms 3 different compounds when combined with hydrogen g of nitrogen will combine with g, g, and g of oxygen to make them. These observations confirm which letter(s)? 1.0 L of hydrogen gas reacts with 0.5 L of oxygen gas to form 1.0 L of water vapor. This observation illustrates which letter(s)? The person named in this letter enjoyed teaching you in Chem 5 and hopes you enjoy your break. A. Prof. Hair B. Law of Conservation of Mass C. Law of Multiple Proportions D. Law of Combining Volumes E. Law of Definite Proportions F. Avogadro s Hypothesis G. The Octet Rule H. Charles Law I. Boyle s Law J. Ideal Gas Law K. Dalton s Law of Partial Pressures L. Kinetic Molecular Theory M. Maxwell-Boltzmann Distribution N. First Law of Thermodynamics O. Hess s Law P. Second Law of Thermodynamics Q. Third Law of Thermodynamics R. Law of Mass Action S. LeChatelier s Principle T. Hydrolysis Reaction U. Common Ion Effect _