PERIODIC TABLE OF THE ELEMENTS

Transcription

1 Chem 114 Exam 3 April 4, 2016 Name: PLEASE print your name on the exam and sign the academic integrity pledge. Print your name and fill in the circles with your I.D. # on side 1 (blue) of the scantron. Please mark answers on both the exam and scantron, and show work on the exam. Do not write any chemistry notes on the scantron. Since students have the scantrons in advance, this could be grounds for an academic dishonesty inquiry. Only non-programmable calculators may be used on this exam. The use of cell phones, headphones, programmable calculators (TI and similar models), or any other electronic devices will be considered grounds for an academic dishonesty inquiry, as defined in the Conduct section of the University of South Dakota Student Handbook. I will not copy from another student s exam nor will I knowingly allow another student to copy from my exam. I also will not use any forbidden sources of information on this exam, such as written notes, etc. Instructor will complete: Signature Equations: K w = 1.0 x = [H + ][OH - ] = K a K b ph=pk a + log [A- ] [HA] Constants: R = J/(mol K) PERIODIC TABLE OF THE ELEMENTS 1

2 Multiple Choice: 1. Calculate the ph of a solution that contains 4.2 x 10-3 M H +. A) 4.38 B) 2.38 C) 2.53 D) 3.0 E) If you added some HNO 3 to water, would you expect the ph of the solution to be. A) greater than 7 B) less than 7 C) equal to 7 D) equal to 14 E) none of these 3. What is the conjugate acid of HSO 4 -? A) SO 4 2- B) H 2 SO 4 C) H 3 O + D) OH - E) H 2 O 4. Calculate the hydrogen ion concentration in a solution with ph = A) 5.47 M B) 8.53 M C) 3.39 x 10-4 M D) 2.95 x M E) 2.95 x 10-9 M 5. Calculate the ph of a solution with [OH - ] = 1.0 x A) 9.00 B) 8.00 C) 4.00 D) 5.00 E) Calculate the ph of a M HClO 4 solution. A) B) C) 1.60 D) 9.50 E) Which of the following is an example of an organic acid? A) R-NH 2 B) R-CO 2 H C) HCl D) NaOH E) H 2 O 8. CH 3 CH 2 NH 3 + is. A) an acid B) a base C) a buffer D) a salt E) bivalent 9. For nitrous acid, HNO 2, the acid dissociation constant is 4.0 x Calculate the ph of 0.25 M HNO 2. A) 2.00 B) 2.30 C) 2.70 D) 3.70 E) none of these 2

3 10. In the following reaction in aqueous solution, the acid reactant is, and its conjugate base product is. CH 3 NH 2 + HNO 3 CH 3 NH NO 3 (A) CH 3 NH 2 ; CH 3 NH 3 + (B) CH 3 NH 2 ; NO 3 (C) HNO 3 ; CH 3 NH 3 + (D) HNO 3 ; NO For any weak acid, the percent ionization for 0.1 M HA is the percent dissociation for 1.0 M HA. A) greater than B) less than C) equal to D) not enough information 12. The hydrogen sulfate or bisulfate ion HSO 4 can act as either an acid or a base in water solution. In which of the following equations does HSO 4 act as an acid? A) HSO 4 + H 2 O H 2 SO 4 + OH B) HSO 4 + H 3 O + SO 3 + 2H 2 O C) HSO 4 + OH H 2 SO 4 + O 2 D) HSO 4 + H 2 O SO H 3 O + E) none of these 13. The stronger the acid, (A) the stronger its conjugate base. (B) the weaker its conjugate base. (C) the more concentrated the acid. (D) the less concentrated the conjugate base. (E) the more concentrated the conjugate base. 14. Using the following K a values, indicate the correct order of acid strength. HCl none available HNO 2 K a = 4.0 x 10 4 HCN K a = 6.2 x A) HCN > HNO 2 > H 3 O + > HCl B) HCl > H 3 O + > HCN > HNO 2 C) H 3 O + > HCl > HNO 2 > HCN D) HCl > H 3 O + > HNO 2 > HCN 15. The conjugate base of a weak acid is A) a strong base B) a weak base C) a strong acid D) a weak acid E) none of these 16. Calculate the poh of a 5.0 M solution of HCl. A) B) 0.70 C) D) E) none of these 3

4 17. Which of the following is the equilibrium constant expression for the dissociation of the weak acid HOCl? A) K = [H+ ][OCl ] [HOCl] B) K = [H + ][OCl ] [HOCl] C) K = [H + ][OCl ] D) K = [H+ ][O 2 ][Cl ] [HOCl] E) none of these 18. The K b for NH 3 is 1.8 x What is the K a for NH 4 +? A) 5.6 x 10 4 B) 5.6 x C) 1.8 x 10-5 D) 1.8 x 10-9 E) none of these 19. Would you expect CCl 3 CO 2 H or CH 3 CO 2 H to have the larger K a,? A) CCl 3 CO 2 H B) CH 3 CO 2 H C) The K a values would be equal. 20. Which of the following statements is/are true of buffer solutions: I. A buffer maintains a constant ph. II. A buffer solution reacts with added acid. III. A buffer solution reacts with added base. IV. A buffer is a mixture of a weak base and its conjugate acid. V. A buffer is a mixture of a weak acid and its conjugate base. A) I, V B) I, IV, V C) I, II, III D) V E) All are true. 21. The ph of an aqueous solution that is 0.10 M HCO 2 H (K a = 1.8 x 10-4 ) and 0.10 M NaHCO 2 is A) 5.62 B) 2.38 C) 3.74 D) 8.38 E) The ph at the equivalence point for a titration of 25 ml of 0.1 M CH 3 CO 2 H (K a = 1.8 x 10-5 ) with 0.05 M NaOH would be: A) less than 7 B) greater than 7 C) equal to 7 D) not enough information 23. Two drops of indicator HIn (pk a = 9.0), where HIn is yellow and In - is blue, are placed in ml of 0.10 M NaOH. What color is the solution? A) yellow B) blue C) green D) red E) colorless 4

5 24. For the titration curve shown to the right, which statement is true: (A) The curve shows the titration of a weak acid with a strong base. (B) The curve shows the titration of a strong acid with a strong base. (C) The curve shows the titration of a weak base with a strong acid. (D) The curve shows the titration of weak base with a strong base. 25. The titration curve shown to the right is for the titration of 35 ml of 0.2 M HCl using a strong base as the titrant. What is the equivalence point volume? (A) 60 ml (B) 25 ml (C) 35 ml (D) Without knowing the concentration of the strong base, we cannot determine the equivalence point volume. 26. For the titration curves shown to the right, which statement is true: A) Titration curve (a) is for the titration of the weakest acid. B) Titration curve (f) is for the titration of the weakest acid. C) Titration curve (a) is for the titration of the weakest base. D) Titration curve (f) is for the titration of the weakest base. 27. Which of the following would be the best choice for preparing a buffer with a ph equal to 9? (A) Acetic acid, K a = 1.6 x 10-5 (B) Formic acid, K a = 1.77 x 10-4 (C) Boric acid, K a = 5.4 x (D) HIO, K a = 2.3 x

6 28. Calculate the solubility of PbI 2 (s) in water given the K sp value for PbI 2 (s) is equal to 8.5 x (A) 1.3 x 10 3 (B) 2.0 x 10 3 (C) 1.6 x 10 3 (D) 9.2 x The solubility of AgBr(s) is 7.35 x 10-7 M in pure water. Would the solubility increase, decrease, or stay the same in a solution of KBr? (A) increase (B) decrease (C) stay the same 6