E) Buffer capacity is the amount of acid that can be added until all of the base is used up.

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1 Chem 124 Spring 2016 Exam 3 VERSION 1 Name make sure you fill in your version number in the TN box on the side of your scantron sheet 1) Which of the following solutions is a good buffer system? A) a solution that is 0.10 M HC 2 H 3 O 2 and 0.10 M LiC 2 H 3 O 2 B) a solution that is 0.10 M HCl and 0.10 M NH 4 + C) a solution that is 0.10 M NaOH and 0.10 M KOH D) a solution that is 0.10 M HF and 0.10 M NaC 2 H 3 O 2 E) None of the above are buffer systems. 2) Which one of the following statements is true? A) A buffer can absorb an unlimited amount of acid or base. B) A buffer is an aqueous solution composed of two weak acids. C) A buffer does not change ph when strong acid or base is added. D) A buffer resists ph change by neutralizing added acids and bases. E) None of the above are true. 3) If the pk a of HCHO 2 is 3.74 and the ph of an HCHO 2 /NaCHO 2 solution is 3.11, which of the following is true? ( >> means more than 100x << means less than 100x A) [HCHO 2 ] << [NaCHO 2 ] B) [HCHO 2 ] < [NaCHO 2 ] C) [HCHO 2 ] = [NaCHO 2 ] D) [HCHO 2 ] > [NaCHO 2 ] E) It is not possible to make a buffer of this ph from HCHO 2 and NaCHO 2. 4) You wish to prepare an HC 2 H 3 O 2 buffer with a ph of If the pk a of is 4.74, what ratio of C 2 H 3 O 2 /HC 2 H 3 O 2 must you use? A) 0.20 B) 1.0 C) 0.70 D) 5.0 E) 1.1 5) Define buffer capacity. A) Buffer capacity is the amount of base that can be added until all of the acid is used up. B) Buffer capacity is the amount of acid that can be added until all of the acid is used up. C) Buffer capacity is the amount of base that can be added until all of the base is used up. D) Buffer capacity is the amount of acid or base that can be added to a buffer without destroying its effectiveness. E) Buffer capacity is the amount of acid that can be added until all of the base is used up. 6) Which of the following acids (listed with K a values) and their conjugate base would form a buffer with a ph of 2.34? A) HClO, K a = B) HClO 2, K a = C) HC 7 H 5 O 2, K a = D) HCN, K a = E) HF, K a =

2 7) A solution containing AgNO 3 is mixed with a solution of NaCl to form a solution that is 0.10 M in AgNO 3 and M in NaCl. What will happen once these solutions are mixed? K sp (AgCl) = A) Silver chloride will precipitate out of solution, leaving an unsaturated solution of AgCl. B) Nothing will happen since NaCl and AgNO 3 are both soluble compounds. C) Nothing will happen since the molar solubility of AgCl is higher than the solution concentrations. D) Silver chloride will precipitate out of solution, leaving a saturated AgCl solution. E) There is not enough information to say anything about this solution. 8) The molar solubility of ZnS is M in pure water. Calculate the K sp for ZnS. A) B) C) D) E) ) Determine the molar solubility of PbSO 4 in pure water. K sp (PbSO 4 ) = A) M B) M C) M D) M E) M 10) A ml sample of 0.10 M Ca(OH) 2 is titrated with 0.10 M HBr. Determine the ph of the solution before the addition of any HBr. A) 0.70 B) 1.00 C) 7.00 D) E) ) Give the expression for the solubility product constant for the sparingly soluble solid BaF 2. A) [BaF 2 ] [Ba 2+ ][F ] 2 B) [Ba 2+ ][F ] C) [Ba 2+ ][F ] 2 D) [Ba 2+ ] 2 [F ] E) [Ba2+ ][F ] 2 [BaF 2 ] 12) Which of the following compounds will have the highest molar solubility in pure water? A) MgCO 3, K sp = B) PbSO 4, K sp = C) FeS, K sp = D) PbS, K sp = E) AgI, K sp = ) Calculate the ph of a solution that contains M OH at 25 C. A) B) 8.89 C) 9.64 D) 1.28 E) ) Consider a reaction that has a positive H and a positive S. Which of the following statements is true? A) This reaction will be spontaneous only at high temperatures. B) This reaction will be spontaneous at all temperatures. C) This reaction will be nonspontaneous at all temperatures. D) This reaction will be nonspontaneous only at high temperatures. E) It is not possible to determine without more information. 2

3 15) Determine G rxn using the following information. H 2 (g) + CO(g) CH 2 O(g) H = +1.9 kj; S = J/K A) kj B) kj C) kj D) kj E) kj 16) Which of the following processes has a S < 0? A) Water freezes. B) methanol (g, at 555 K) methanol (g, at 400 K) C) Isopropyl alcohol condenses. D) carbon dioxide(g) carbon dioxide(s) E) All of the above processes have a S < 0. 17) Choose the statement below that is true. A) If K < 1, the reaction is at equilibrium. B) If K < 1, the reaction is spontaneous in the reverse direction. C) If K < 1, the reaction is spontaneous in the forward direction. D) Not enough information is given. 18) If G < 0, which of the following statements is true? A) The reaction is not spontaneous. B) The reaction is at equilibrium. C) The reaction is spontaneous. D) Not enough information is given. 19) Calculate S rxn for the following reaction. The S for each species is shown below the reaction. C 2 H 2 (g) + H 2 (g) C 2 H 4 (g) S (J/mol K) A) J/K B) J/K C) J/K D) J/K E) J/K 20) Determine the equilibrium constant for the following reaction at 298 K. SO 3 (g) + H 2 O(g) H 2 SO 4 (l) G = kj A) B) C) D) E) ) Which of the following relationships is correct at constant T and P? A) G > 0 represents a spontaneous process. B) G > 0 represents an increase in kinetic energy. C) G is proportional to - S univ. D) G < 0 represents a nonspontaneous process. E) All of the above are correct. 22) Identify the change in state where S decreases. A) liquid to gas B) gas to solid C) solid to gas D) solid to liquid 3

4 23) Calculate the concentration of OH in a solution that contains M H 3 O+ at 25 C. Identify the solution as acidic, basic or neutral. A) M, neutral B) M, acidic C) M, basic D) M, basic E) M, acidic 24) Calculate the percent ionization of nitrous acid in a solution that is M in nitrous acid. The acid dissociation constant of nitrous acid is A) B) 4.25 C) D) 5.53 E) ) A buffer contains equal amounts of a weak acid and its conjugate base and has a ph of 5.25.Which would be a reasonable value of buffer ph after the addition of a small amount of base? A) 5.35 B) 4.15 C) 6.35 D) ) What can you conclude about G rxn for the reaction at 25 C? H 2 (g) + Br 2 (g) 2 HBr(g) K = A) G rxn > 0 B) G rxn < 0 C) G rxn = 0 D) There is not enough information to determine the sign or magnitude of G rxn. 27) What element is being reduced in the following redox reaction? H 2 O 2 (l) + ClO 2 (aq) ClO 2 (aq) + O 2 (g) A) O B) C C) H D) Cl E) N 28) Which of the following is true? A) At the equivalence point, the ph is always 7. B) A titration curve is a plot of ph vs. the [base]/[acid] ratio. C) The equivalence point is where the amount of acid equals the amount of base during any acid-base titration. D) An indicator is not ph sensitive. E) None of the above are true. 29) Which of the following processes shows a decrease in entropy of the system? A) CH 3 OH(l) CO(g) + 2H 2 (g) B) 2 NO(g) + O 2 (g) 2 NO 2 (g) C) COCl 2 (g) CO(g) + Cl 2 (g) D) NaClO 3 (s) Na + (aq) + ClO 3 - (aq) E) None of the above will show a decrease in entropy. 4

5 30) Identify oxidation. A) increase in oxidation number B) loss of electrons C) decrease in oxidation number D) gain of electrons E) both A and B 31) Consider a reaction that has a negative H and a negative S. Which of the following statements is true? A) This reaction will be spontaneous only at high temperatures. B) This reaction will be spontaneous at all temperatures. C) This reaction will be nonspontaneous at all temperatures. D) This reaction will be nonspontaneous only at high temperatures. E) It is not possible to determine without more information. 32) Identify the change in state that does not have an increase in entropy. A) water freezing B) dry ice subliming C) water boiling D) water evaporating E) ice melting 33) How many electrons are transferred in the following reaction? (The reaction is unbalanced.) Ca(s) + Cr 3+ (aq) Cr(s) + Ca 2+ (aq) A) 6 B) 2 C) 1 D) 3 E) 4 34) What element is being oxidized in the following redox reaction? Mg 2+ (aq) + NH 4 + (aq) Mg(s) + NO3 (aq) A) H B) Mg C) N D) O 35) What element is being reduced in the following redox reaction? MnO 4 (aq) + H 2 C 2 O 4 (aq) Mn 2+ (aq) + CO 2 (g) A) Mn B) O C) H D) C 36) Under which of the following conditions would one mole of He have the highest entropy, S? A) 127 C and 25 L B) 127 C and 15 L C) 17 C and 25 L D) 17 C and 15 L 37) The oxidation state of S in Na 2 SO 4 A) +6 B) -6 C) +2 D) -2 38) Copper(II) chloride is highly soluble in water. This compound has. A) high equilibrium constant B) low solubility product C) high dissociation constant D) high solubility product 5

6 Match the following. 39) ph = 7 40) ph = pk a 41) ph > 7 42) ph < 7 A) equivalence point of a strong acid/strong base titration B) half-way to equivalence point of a weak acid/strong base titration C) equivalence point of a weak acid/strong base titration D) equivalence point of a weak base/strong acid titration Match the following. 43) Arrhenius acid 44) Arrhenius base 45) Br nsted-lowry acid 46) Br nsted-lowry base 47) Lewis acid 48) Lewis base A) produces protons in aqueous solution B) produces hydroxide ions in aqueous solution C) proton donor D) proton acceptor E) electron pair acceptor F) electron pair donor 49) Explain the common ion effect with respect to molar solubility. Use as an example the dissolving of AgI in water. What effect would the addition of NaI have on the solubility of the AgI? 6

7 50) Why can't we say that a spontaneous reaction is a fast reaction? 51) Balance the following redox reaction if it occurs in acidic solution. Cd(s) + Ag + (aq) Ag(s) + Cd 2+ (aq) 7

8 52) Determine G rxn using the following information. FeO(s) + CO(g) Fe(s) + CO 2 (g) H = kj; S = J/K 8

9 53) Use Hess's law to calculate G rxn using the following information. CO(g) C(s) + 1/2 O 2 (g) G rxn =? CO 2 (g) C(s) + O 2 (g) CO(g) + 1/2 O 2 (g) CO 2 (g) G rxn = kj G rxn = kj 9

10 Answer Key Testname: CHEM124SPRING2014EXAM3_V1 1) A 2) D 3) D 4) D 5) D 6) B 7) D 8) C 9) A 10) E 11) C 12) A 13) B 14) A 15) A 16) E 17) B 18) C 19) E 20) A 21) C 22) B 23) E 24) B 25) A 26) B 27) D 28) C 29) B 30) E 31) D 32) A 33) A 34) C 35) A 36) A 37) A 38) D 39) A 40) B 41) C 42) D 43) A 44) B 45) C 46) D 47) E 48) F 10

11 Answer Key Testname: CHEM124SPRING2014EXAM3_V1 49) The common ion effect occurs when a solubility equilibrium is shifted due to a second compound that contains an ion common with the first. For example, the molar solubility of MA (MA M + + A - ) would be higher in pure water than if MA were dissolved in an aqueous solution that already contained another compound with A -. MA M + + A - 50) Spontaneity is a thermodynamic quantity that determines if a reaction will occur and to what extent. The speed of a reaction is not related to the spontaneity. A spontaneous reaction can be very slow. 51) 52) 53) 11

Chem 401 Unit 3 Exam F18 (Buffers, Titrations, Ksp, Transition Metals & Electrochemistry)

Seat #: Date: Chem 401 Unit 3 Exam F18 (Buffers, Titrations, Ksp, Transition Metals & Electrochemistry) Multiple Choice Identify the choice that best completes the statement or answers the question. (4.2pts