3. [7 points] Which of the following slightly soluble salts has the largest molar solubility in aqueous solution?

Transcription

1 1. [7 points] The solubility product expression for Pb 3 (PO 4 ) 2 (s) is (a) [3 Pb 2+ ] 3 [2 PO 4 3 ] 2 (b) [Pb 2+ ] 2 [PO 4 3 ] 3 (c) [3 Pb 2+ ] 3 [2 PO 4 3 ] 2 /[Zn 3 (PO 4 ) 2 ] (d) [3 Pb 2+ ][2 PO 4 3 ] (e) [Pb 2+ ] 3 [PO 4 3 ] 2 2. [7 points] What is the molar solubility of Ag 2 CO 3 in water? (K sp = 8.1 x ) (a) 1.3 x 10 4 M (b) 2.6 x 10 4 M (c) 2.0 x 10 4 M (d) 2.8 x 10 6 M (e) 8.1 x M 3. [7 points] Which of the following slightly soluble salts has the largest molar solubility in aqueous solution? (a) CdCO 3 K sp = 5.2 x (b) Cd(OH) 2 K sp = 2.5 x (c) Co(OH) 2 K sp = 2.5 x (d) AgI K sp = 8.3 x (e) ZnCO 3 K sp = 1.4 x [7 points] Which of the following slightly soluble salts would not be more soluble in acidic solution? (a) CdCO 3 K sp = 5.2 x (b) Cd(OH) 2 K sp = 2.5 x (c) Co(OH) 2 K sp = 2.5 x (d) AgI K sp = 8.3 x (e) ZnCO 3 K sp = 1.4 x 10 11

2 5. [7 points] Calculate the molar solubility of Cd(OH) 2 when buffered at a ph = The K sp for Cd(OH) 2 is 2.5 x (a) 8.5 x 10 6 M (b) 6.3 x M (c) 1.3 x M (d) 5.0 x 10 2 M (e) 1.8 x 10 5 M 6. [7 points] A solution contains M AsO 4 3, M I, and M CO 3 2. If AgNO 3 is slowly added, in what order would the silver salts precipitate? Ag 3 AsO 4, K sp = 1.0 x AgI, K sp = 8.3 x Ag 2 CO 3 K sp = 8.1 x (a) 1 st : Ag 2 CO 3 2 nd : Ag 3 AsO 4 3 rd : AgI (b) 1 st : Ag 3 AsO 4 2 nd : Ag 2 CO 3 3 rd : AgI (c) 1 st : AgI 2 nd : Ag 3 AsO 4 3 rd : Ag 2 CO 3 (d) 1 st : AgI 2 nd : Ag 2 CO 3 3 rd : Ag 3 AsO 4 (e) 1 st : Ag 2 CO 3 2 nd : AgI 3 rd : Ag 3 AsO 4 7. [7 points] What is the concentration of free cobalt ion if 5.25 x 10 4 moles of Co(NO 3 ) 2 is added to 1.00 L of 3.0 M NH 3 solution? The K f for the formation of Co(NH 3 ) 6 2+ is 8.3 x (a) 2.1 x 10 9 M (b) 3.2 x 10 4 M (c) 5.3 x 10 4 M (d) 8.7 x M (e) 1.2 x 10 5 M 8. [7 points] The solubility of which of the following salts will be least sensitive to ph? (a) KClO 4 (b) BaF 2 (c) FePO 4 (d) NiCO 3 (e) The solubility of all four salts will be dramatically affected by ph.

3 9. [7 points] How many of the following reagents would increase the solubility of Ni(OH) 2 (s)? Ni(NO 3 ) 2 NaOH HCl NH 3 (a) none (b) one (c) two (d) three (e) four 10. [7 points] Which of the following substances that we use during experiment #25 does not act as an oxidizing agent. (a) Aqua regia (b) Hydrochloric acid (c) Hydrogen peroxide (d) Choose this answer if none of the above are used as oxidizing agents (e) Choose this answer if all of the above are used as oxidizing agents 11. [7 points] How is Zn 2+ isolated from a mixture containing ZnS(s), NiS(s), and CoS(s)? (a) ZnS dissolves when concentrated NH 3 is added to form the Zn(NH 3 ) 4 2+ complex ion. (b) The solution is made to be distinctly acidic by adding concentrated HCl, which dissolves the ZnS and leaves the NiS and CoS as solids. (c) Due to the large difference in K sp values, dilute NaOH is carefully added to make the solution slightly basic, which dissolves the ZnS and leaves the NiS and CoS as a solid. (d) Ice cold 1 M HCl is added, which dissolves the ZnS and leaves the NiS and CoS as solids. (e) Aqua regia is used because it will dissolve the ZnS and leave the NiS and CoS as solids.

4 12. [7 points] A student performed laboratory tests on the solubility of slightly soluble salts A, B, and C in water as a function of temperature. The results of these tests are shown below. Based on this data which of the following statements regarding the separation of these salts is correct? Solubility (g/l) Temp. (C) A B C (a) For all three salts, the temperature has a minimal effect on the solubility. (b) The basis for separation of salt C from salts A and B is that salt C will dissolve in hot water and salts A and B will not. (c) In order to separate salts A and B, the precipitates should be heated in water and the resulting solution must be separated quickly from the remaining solid to avoid reprecipitation as the solution cools. (d) It would be easiest to separate salt A from salt C at low temperatures. (e) Changing the temperature of the solution is not a practical way to separate any of the three salts. 13. [7 points] The Group II ions are precipitated from acidic solution as sulfides. The precipitating reagent is 5 % thioacetamide and heating to 80 C produces a saturated solution of hydrogen sulfide with the concentration of H 2 S being 0.10 M. Calculate the molar concentration of HS in a solution that is saturated with H 2 S and made acidic with concentrated 0.3 M HNO 3. The K a1 for H 2 S (H 2 S H + + HS ) is K a2 is sufficiently small that we can assume no H 2 S molecules lose two protons. (a) 3 x 10 8 (b) 3 x 10 7 (c) 3 x 10 6 (d) 3 x 10 5 (e) 3 x 10 4

5 14. [7 points] If the metal ion concentrations are estimated to be 0.01 M, which of the following sulfides would precipitate from the solution described in question 13? Remember that K sp values for a metal sulphide, MS, are determined from the following equation: MS(s) + H 2 O(l) M 2+ (aq) + HS (aq) + OH (aq) CoS PbS CuS SnS FeS K sp = K sp = K sp = K sp = K sp = (a) CuS only (b) CuS and PbS (c) CoS and FeS (d) CuS, PbS, and SnS (e) CoS, CuS, FeS, PbS, and SnS Use the following information to answer problems A student is given a test tube containing one or more of the following cations in solution: Ag +, Cu 2+, Fe 3+, Ni 2+, and Zn 2+. She then performs the following analysis: 1. Cold, dilute HCl is added to the solution. This results in the formation of a white precipitate and a blue-green decantate. The decantate is transferred to a clean dry test tube for further analysis (step 2). 2. The decantate obtained in step 1 is treated with HNO 3 and H 2 S. This results in the formation of a dark precipitate and a green decantate. The decantate is transferred to a clean dry test tube for further analysis (step 3). 3. The solution obtained in step 2 was treated with NH 3 and NH 4 Cl. This results in the formation a dark, rust colored precipitate and a blue solution. 15. [7 points] Which cations are present in the dark, rust colored precipitate formed in step 3? (a) Fe 3+, Cu 2+, Ni 2+ and Fe 3+ (b) Fe 3+ and Cu 2+ (c) Fe 3+ (d) Fe 3+ and Ni 2+ (e) Ni 2+ and Cu 2+

6 16. [7 points] What can we say about the cations present in the blue solution formed in step 3? (a) Cu 2+ is definitely present, no other ions may be present (b) Ni 2+ is definitely present, no other ions may be present (c) Cu 2+ and Ni 2+ are definitely present, no other ions may be present (d) Ni 2+ and Zn 2+ are definitely present, no other ions may be present (e) Ni 2+ is definitely present, Zn 2+ maybe present, no other ions may be present 17. [7 points] From the initial list which ions can we say are definitely present? (a) Ag +, Cu 2+ and Fe 3+ (b) Ag +, Cu 2+, Ni 2+ and Fe 3+ (c) Ag +, Ni 2+ and Fe 3+ (d) Cu 2+, Ni 2+ and Fe 3+ (e) Zn 2+, Ag +, Cu 2+, Ni 2+ and Fe [7 points] A solution contains M Al 3+ and M Ag +. Solid Na 3 PO 4 is slowly added to separate the two cations. The K sp for AlPO 4 is 9.8 x and K sp for Ag 3 PO 4 is 8.9 x Which precipitate will form first and what is the concentration of PO 4 3 when the second precipitate begins to form? (a) AlPO 4 will form first; [PO 4 3 ] = 6.5 x M (b) AlPO 4 will form first; [PO 4 3 ] = 2.6 x M (c) Ag 3 PO 4 will form first; [PO 4 3 ] = 6.5 x M (d) Ag 3 PO 4 will form first; [PO 4 3 ] = 2.6 x M (e) no ppt will form 19. [7 points] Which of the following is always positive when a spontaneous process occurs? (a) G system (b) G surroundings (c) G universe (d) S system (e) S universe

7 20. [7 points] Which of the following substances will have the largest standard molar entropy, S? (a) HCl (l) (b) HCl (s) (c) HCl (g) (d) HBr (g) (e) HI (g) 21. [7 points] Consider the reaction: NH 3 (g) + HCl(g) NH 4 Cl(s) Given the following table of thermodynamic data at 298 K: Substance H f (kj/mol) S (J/mol*K) NH 3 (g) HCl(g) NH 4 Cl(s) The value of G for the reaction is. (a) 91.1 kj (b) 34.7 kj (c) kj (d) kj (e) 8.50 x 10 3 kj 22. [7 points] Given the fact that the following reaction is exothermic. N 2 (g) + 3 H 2 (g) 2 NH 3 (g) What can we say about the spontaneity of this reaction? (a) spontaneous at all temperatures (b) spontaneous only at high temperatures (c) spontaneous only at low temperatures (d) non spontaneous at all temperatures (e) more information is need to predict if the reaction is spontaneous

8 23. [7 points] Consider the following five reactions. S is positive for reaction(s). BaF 2 (s) Ba 2+ (aq) + 2F (aq) 2 H 2 (g) + O 2 (g) 2 H 2 O(g) H 2 O(l) H 2 O(s) 2 SO 3 (g) 2 SO 2 (g) + O 2 (g) 2 Hg(l) + O 2 (g) 2 HgO(s) (a) one (b) two (c) three (d) four (e) five 24. [7 points] From the following H and S values predict which of the following hypothetical reactions would be spontaneous at 27 C. H (kj/mol) S (J/mol*K) Reaction I Reaction II Reaction III (a) I only (b) I and II (c) I and III (d) II and III (e) I, II, and III 25. [7 points] The K f = 1.7 x 10 7 for the following reaction at 25 C. Calculate the value of G in kj/mol. Ag + (aq) + 2 NH 3 (aq) Ag(NH 3 ) 2 + (aq) (a) 41.3 kj/mol (b) kj/mol (c) 3.46 kj/mol (d) kj/mol (e) kj/mol

9 Useful Equations: G = H T S Gº rxn = Σn Gº f (products) Σm Gº f (reactants) G = Gº + RT ln(q) K eq = exp[ Gº/RT]