1. (3) The pressure on an equilibrium mixture of the three gases N 2, H 2 and NH 3

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1 1. (3) The pressure on an equilibrium mixture of the three gases N 2, H 2 and NH 3 N 2 (g) + 3 H 2 (g) 2 NH 3 (g) is suddenly decreased by doubling the volume of the container at constant temperature. Which of the following will be true when the system returns to equilibrium? a) the concentration of NH 3 will have increased b) the value of K p will have increased c) the number of moles of H 2 will have increased. d) the number of moles of NH 3 will have increased. e) the value of K will have increased. 2. (4) At 55 o C, K = 2.04 x for the reaction 2 SO 2 + O 2 (g) 2 SO 3 (g) If mol SO 2 (g) and mol O 2 (g) are placed in a 1.00 L container at this temperature, the equilibrium concentration of SO 3 (g) will be: a) 2.02 x M b) 2.02 x10 11 M c) 4.04 x M d) 4.08 x M e) 4.08 x (4) At 25 o C, the equilibrium mixture of the reaction 2 NO (g) + O 2 (g) 2 NO 2 (g) contains mol of NO 2, mol of NO and mol of O 2 in a 4.00 L bulb. What is the value of K at 25 o C for this reaction? a) b) 14 c) 9.4 d) 3.5 e) 2.3 Page 21

2 4. (4) At 25 o C, K P = 9.0 for the reaction: H 2 (g) + I 2 (g) 2 HI (g) At this temperature, 1.50 mol of HI and 0.50 moles each of H 2 and I 2 are placed in a 1.00 L flask. Approximately how many moles of I 2 will be present when the system comes to equilibrium? a) 0.01 b) 0.05 c) 0.10 d) 0.50 e) (3) How many of the following statements about the reaction quotient, Q, are true? I. The reaction quotient may sometimes by zero. II. The reaction quotient may be larger than the equilibrium constant. III. The reaction quotient may be smaller than the equilibrium constant. IV. The numerical value of the reaction quotient changes with time as a reaction proceeds. a) 1 b) 2 c) 3 d) all of them e) none of them 6. (3) For which of the following reactions is the equilibrium constant equal to K b? a) NH 3 (aq) + HCOOH (aq) NH 4 + (aq) + HCOO (aq) b) CH 3 NH 2 (aq) + H 2 O CH 3 NH 3 + (aq) + OH (aq) c) OH (aq) + CH 3 COOH (aq) H 2 O + CH 3 COO (aq) d) CH 3 NH 2 (aq) + H 3 O + (aq) CH 3 NH 3 + (aq) + H 2 O e) H 3 O + (aq) + OH (aq) 2 H 2 O 7. (3) For the reaction: CO 2 (g) + H 2 (g) CO(g) + H 2 O(l) which of the following statements is true? a) K P = K b) K P = K x RT c) K P = K/RT d) Adding more H 2 O(l) will shift the equilibrium to the left e) Decreasing the volume of the container will have no effect on this system Page 22

3 8. (3) Consider the data below, for the autoionization of water: 2 H 2 O(l) H 3 O + (aq) + OH (aq) T ( o C) K w x x x Which of the following statements is false? a) The autoionization of water is endothermic b) At 50 o C, [H 3 O + ] is 2.34 x 10 7 M c) At 50 o C, [H 3 O + ] = [OH ] d) At 50 o C, ph + poh = 14.0 e) The [H 3 O + ] in water increases with increasing temperature 9. (3) How many of the following changes will shift the equilibrium to the left? I. Lowering the ph of : Al(H 2 O) 3+ 6 (aq) AlOH. (H 2 O) H + (aq) II. Raising the temperature of: N 2 F 4 (g) 2 NF 2 (g) H = 38.5 kj III. Transferring the reaction to a larger vessel: 3O 2 (g) 2O 3 (g) IV. Adding PbS (s) to: 2 PbS (s) + 3 O 2 (g) 2 PbO (s) + 2 SO 2 (g) a) 1 b) 2 c) 3 d) 4 e) none of them 10. (3) Shown below are pairs of bases. In which pair is the weaker base written first? a) NO 3, NO 2 d) PO 4 3, H 2 PO 4 2 b) OH, F c) HPO 4 2, H 2 PO 4 e) S 2, HS Page 23

4 Consider the following acids and their K a values to answer the next two (2) questions. I. + NH x II. HC 2 O x 10 5 III. HIO x 10 1 IV. 2 HPO x V. HOCl 3.5 x (3) Which of these species is/are amphoteric? a) II, IV b) II, V c) III, IV d) I only e) I, II and IV 12. (3) Rank the conjugate bases of these acids in order of increasing base strength. (weakest base to strongest base) a) II < I < V < IV < III b) III < II < V < I < IV c) II < I < IV < V < III d) IV < I < V < II < III e) III < V < IV < I < II 13. (3) A weak base, B, has a conjugate acid, BH +, which has a K a = 8.8 x What is the ph of a M solution of the base, B? a) 4.32 b) 4.60 c) 7.00 d) 9.40 e) (4) A solution of HOI, with a K a = 2.0 x 10 11, has a ph = Calculate the approximate number of moles of the acid that was added to L of water to make this solution. a) 0.02 b) 0.05 c) 0.09 d) 0.11 e) (3) When 1.0 moles of a weak base, B, is dissolved in 4.0 L of water, the equilibrium concentration of B is found to be 0.20 M. The K b for B is: a) 1.0 x 10 2 b) 1.3 x 10 2 c) 0.80 d) 3.2 e) 72 Page 24

5 Formic acid HCO 2 H, is a weak acid that ionizes in water as follows: HCO 2 H (aq) + H 2 O CO 2 H (aq) + H 3 O + A M solution of HCO 2 H is 3.87 % ionized at 25 o C. Use this information to answer the next two (2) questions. 16. (4) Calculate the K a. a) b) c) 1.5 x 10 3 d) 1.8 x 10 4 e) 2.6 x (4) Calculate the ph of the solution. a) 0.92 b) 2.33 c) d) e) (3) Rank the following 2.0 M solutions in order of increasing ph. NaNO 3 KClO 2 (C 5 H 5 ) 2 NH 2 ClO 4 a) NaNO 3 < KClO 2 < (C 5 H 5 ) 2 NH 2 ClO 4 b) (C 5 H 5 ) 2 NH 2 ClO 4 < NaNO 3 < KClO 2 c) (C 5 H 5 ) 2 NH 2 ClO 4 < KClO 2 < NaNO 3 d) KClO 2 < NaNO 3 < (C 5 H 5 ) 2 NH 2 ClO 4 e) KClO 2 < (C 5 H 5 ) 2 NH 2 ClO 4 < NaNO (3) Four different bases, shown below, are titrated with 0.2 M HCl. Which solution will have the lowest ph at the equivalence point? I. NaOH II. NH 3 (K b = 1.8 x 10 5 ) III. HONH 2 (K b = 1.1 x 10 8 ) IV. C 5 H 5 N (K b = 1.7 x 10 9 ) a) I b) II c) III d) IV e) All of the solutions will be neutral (ph = 7.0) Page 25

6 20. (3) We learned that calcium carbonate is an insoluble salt. In fact, is it slightly soluble in water, in the equilibrium reaction shown below: CaCO 3 (s) Ca 2+ (aq) + CO 3 2 (aq) K sp = 8.7 x 10 9 at 25 o C H = 248 kj/mol Which of the following treatments will lead to an increase in the mass of CaCO 3 (s)? a) Adding more water to the container b) Letting water evaporate from the container c) Increasing the external pressure to 2 atmospheres d) Putting the system into a vacuum e) Changing the temperature to 35 o C 21. (3) The equilibrium constant for the reaction HOCl (aq) + OC 6 H 5 (aq) HOC 6 H 5 (aq) + OCl (aq) is 5.5 x From the magnitude of the K it can determined that: a) OC 6 H 5 is a stronger base than OCl b) HOC 6 H 5 is a stronger acid than HOCl c) OC 6 H 5 is a stronger acid than HOC 6 H 5 d) HOCl is a stronger acid than H 3 O + e) OCl is a stronger base than OH 22. (3) A solution is prepared by mixing 500. ml of 0.40 M HOBr (K a = 2.0 x 10 9 ) and 500. ml of 0.10 M Ca(OH) 2. Calculate the ph of the solution. a) 5.00 b) 8.22 c) 8.70 d) 9.17 e) Page 26

7 Answer the following eight (8) questions concerning the titration of ml of 0.50 M benzoic acid, HC 7 H 5 O 2 (K a = 6.4 x 10 5 ) with 0.25 M KOH. Water will be a major species throughout the titration. The other chemical species that can be present during the titration are: I. H + II. OH III. HC 7 H 5 O 2 IV. C 7 H 5 O 2 V. K (4) Calculate the ph before any KOH has been added. a) 0.30 b) 2.25 c) 2.50 d) 2.75 e) (3) Which major species, in addition to water, are present at this point in the titration? a) I b) I and III c) III d) III and IV e) IV 25. (4) Calculate the ph after the addition of 25.0 ml of KOH. a) 3.34 b) 3.72 c) 4.19 d) 4.67 e) (3) Which major species, in addition to water, are present at this point in the titration? a) II and III b) II and V c) III and V d) III e) III, IV and V 27. (4) Calculate the ph at the end point of the titration. a) 5.29 b) 8.44 c) 8.71 d) 8.95 e) (3) Which major species, in addition to water, are present at this point in the titration? a) II, IV and V b) III and IV c) III and V d) II and V e) IV and V 29. (4) Calculate the ph after the addition of a total of 300 ml of KOH. a) b) c) d) e) (3) Which species, in addition to water, are present at this point in the titration? a) II, IV and V b) III and IV c) III and V d) II and V e) IV and V Page 27