Chemistry 112 Name Practice Exam 3C Section

Transcription

1 Chemistry 112 Name Practice Exam 3C Section IMPORTANT: On the scantron (answer sheet), you MUST clearly fill your name, your student number, section number, and test form (white cover = test form A; yellow cover = test form B). Use a #2 pencil. There are 25 questions on this exam. Check that you have done all of the problems and filled in the first 25 bubbles on the scantron. The maximum score on this exam is 25 points. Your score will be reported in percent (max 100%). Exam policy Calculators with text-programmable memory are not allowed. Relevant data and formulas, including the periodic table, are attached at the end of this exam. Your grade will be based only on what is on the scantron form. The answer key will be posted on the web after the exam (on the Exam Schedule page). You must turn in your cover sheet with your scantron answer form. You MUST bubble in all of your answers before the time is up; you may not bubble your scantron after the time is called. Hints As you read the question, underline or circle key words to highlight them for yourself. Avoid errors from "mis-reading" the question. Pay attention to units and magnitudes (decimal places) of numbers obtained from calculations. There is no penalty for guessing.

2 Chem 112 EXAM 3 PRACTICE EXAM 3C SPRING Which one of the following species can offer cathodic protection to prevent the rusting of Fe (s) at 25 o C? A. Na + (aq) B. Br 2 (l) C. H + (aq) D. Ni (s) E. Zn (s) 2. Almandine is the mineral name of the deep red gemstone known as a garnet, and has the formula Fe 3 Al 2 (SiO 4 ) 3, where iron is in the +2 oxidation state. What is the oxidation state of oxygen in almandine? A. 2 B. 1 C. 4 D. 0 E A chemical company uses mercury ions in a production line, and needs to reduce the concentration of toxic Hg 2+ as much as possible before dumping the wastewater. The company decides to try to precipitate the mercury as HgS(s). If the equilibrium concentration of S 2 in the solution is 0.75 M, what is the Hg 2+ concentration in a saturated solution at 25 C? The K sp of HgS is 4.0 x A. 6.3 x M B. 8.4 x M C. 5.3 x M D. 4.0 x M E. 7.1 x M 4. How many electrons are transferred in the following unbalanced redox reaction? A. 1 B. 2 C. 3 D. 5 E. 6 Al (s) + Cd(NO 3 ) 2 (aq) Al(NO 3 ) 3 (aq) + Cd (s)

3 5. What is the ph of a mixture of 2.7 mmol/l HF and 19 mmol/l NaF? K a (HF) = 7.1 x 10 4 A B C D E Much to the surprise of everyone, Nittnium (Nt) can be incorporated into redox reactions! Which species acts as the reducing agent in the following redox reaction? A. Nt 3+ (aq) B. H 2 O (l) C. MnO 2 (s) D. H + (aq) E. MnO 4 (aq) Nt 3+ (aq) + H 2 O (l) + MnO 2 (s) Nt (s) + MnO 4 (aq) + 2H + (aq) 7. For which one of the following titrations would the ph < 7 exactly at the equivalence point? A. HCl titrated with NaOH B. CH 3 COOH (acetic acid) titrated with KOH C. HCN titrated with NaOH D. C 6 H 5 NH 2 titrated with HBr E. HClO 3 titrated with Ca(OH) 2 8. Which one of the following statements is TRUE regarding electrochemistry? A. Electrons flow from the cathode to the anode in electrolytic cells. B. When products are favored in a redox reaction, E o cell is negative, K eq < 1, and ΔG o is positive. C. In a voltaic cell, ΔG = 0 and E cell = 0 at equilibrium. D. In an electrolytic cell, oxidation occurs at the cathode. E. In the salt bridge of a voltaic cell, anions flow towards the cathodic compartment and cations flow towards the anodic compartment.

4 9. Lithium-ion batteries are commonly used in portable devices such as cell phones, laptop computers, and digital cameras because these batteries are light and can be re-charged hundreds of times. Given the two half-reactions involved in a lithium-ion battery below, what is the maximum amount of work the battery can do (in kj) under standard conditions at 25 o C? Half Reaction E o 1/2 (red) (V) Li + (aq) + 1e Li (s) 3.05 Li + (aq) + CoO 2 (s) + 1e LiCoO 2 (s) A kj B x 10 5 kj C kj D x 10 5 kj E kj 10. A titration enthusiast titrates a 500 ml solution of 2 M C 2 H 5 OCOOH (lactic acid) with a 1 M KOH solution for the sheer thrill of titration. What is the ph at the equivalence point at 25 o C? Structure of lactic acid: A. 8.8 B C. 9.1 D. 3.9 E K a of lactic acid = 1.4 x 10 4

5 11. Which of the following slightly soluble salts would be substantially more soluble in an ACIDIC aqueous solution than in pure water at 25 o C? i. Ca 3 (PO 4 ) 2 (s) ii. Fe(OH) 3 (s) iii. AgBr (s) iv. SrCO 3 (s) v. CuI (s) A. ii and v only. B. ii and iv only. C. iii, iv, and v only. D. i, ii, and iv only. E. All of these salts are more soluble in acidic solutions. 12. What is the coefficient in front of water, and is it a product or reactant, when the following redox reaction is balanced in acidic solution? A. 1, reactant B. 1, product C. 2, reactant D. 2, product E. 3, reactant NO (g) + MnO 4 (aq) NO 2 (aq) + MnO 2 (s) 13. Put the following species in order from worst oxidizing agent to best oxidizing agent at 25 o C: A. i < ii < iii B. ii < i < iii C. i < iii < ii D. ii < iii < i E. iii < i < ii i. H 2 O 2 (aq) ii. Li + (aq) iii. F (aq)

6 14. What is the equilibrium constant constant, K eq, for the voltaic cell in the reaction below at 25 o C? A. 4.0 x B. 1.5 x C. 6.9 x D. 2.0 x 10 9 E. 1.4 x Cu(NO 3 ) 2 (aq) + Zn (s) Cu (s) + Zn(NO 3 ) 2 (aq) PLEASE USE THE FOLLOWING ELECTROCHEMICAL CELL DIAGRAM TO ANSWER THE NEXT TWO QUESTIONS: 15. What is the E o cell of the voltaic cell pictured above at 25 o C? A V B V C V D V E V

7 Which of the following actions would cause the cell potential (E cell ) of the voltaic cell pictured above to INCREASE at 25 o C? A. i and iii only. B. ii and iv only. C. i and ii only. D. iii and iv only. E. iv and v only. i. Adding water to the anode. ii. Adding water to the cathode. iii. Increasing the [NaCl] to 2.0 M. iv. Increasing [CuCl 2 ] to 2.5 M. v. Doubling the mass of the Ag (s) electrode. 17. Rick T. Cat needs to make a fancy collar coated with platinum for his Nobel Prize acceptance speech! He decides to utilize electrolysis to electroplate his existing collar (obviously!). How many grams of platinum can be plated over a period of 1 hour if 1 amp of electrical current is used to electrolyze an aqueous solution of PtCl 2 at 25 o C? A g B g C g D g E g 18. Which one of the following processes is the most spontaneous under standard conditions at 25 o C? A. The oxidation of Au (s) B. The oxidation of Cl (aq) C. The oxidation of Na (s) D. The oxidation of Al (s) E. The oxidation of H 2 (g)

8 19. What is the ph of a saturated aqueous solution of Ca(OH) 2 at 25 o C? The K sp of Ca(OH) 2 (s) = 8.0 x A B. 1.9 C D. 1.6 E The data for the titration of a mystery acid with 1 M NaOH is given below. What is the approximate K a of this mystery acid? A. K a = 4.6 x 10 6 B. K a = 1.4 x 10 3 C. K a = 3.7 x 10 7 D. K a = 8.0 x E. K a = 1.8 x 10 5

9 21. Place the following salts in order from lowest molar solubility to highest molar solubility in an aqueous solution at 25 o C: i. BaF 2 (s), K sp = 1.7 x 10 6 A. iii < i < ii B. ii < i < iii C. iii < ii < i D. i < ii < iii E. i < iii < ii ii. CaSO 4 (s), K sp = 2.4 x 10 5 iii. CoS (s), K sp = 4.2 x Which one of the following mixtures would result in a buffer solution at 25 o C? A. 100 ml of 0.5 M HCl ml of 0.5 M NaOH B. 100 ml of 0.5 M NaF ml of 0.5 M HCl C. 50 ml of 0.5 M HF ml of 0.5 M NaOH D. 100 ml of 0.5 M HF + 50 ml of 0.5 M NaOH E. 100 ml of 0.5 M NaF + 50 ml of 0.5 M NaOH 23. An aqueous solution contains a mixture of 0.05 M NaBr, 0.05 M NaF, and 0.05 M KCl. If 1.0 M Pb(NO 3 ) 2 (aq) is added dropwise to this solution, what will be the FIRST solid to start precipitating at 25 o C considering the K sp values in the table below? Salt K sp PbBr 2 (s) 6.6 x 10 6 PbCl 2 (s) 2.4 x 10 4 PbF 2 (s) 4.0 x 10 8 A. Pb (s) B. NaCl (s) C. PbBr 2 (s) D. PbCl 2 (s) E. PbF 2 (s)

10 24. Consider the dissociation of Aspirin (acetylsalicylic acid) below. Which of the following will occur upon the addition of NaOH(aq) to an aqueous solution of Aspirin at 25 o C? i. K a will increase. ii. G will decrease. iii. ph will increase. iv. The concentration of Aspirin will decrease. v. The reaction will shift to the left. A. i and iv only B. ii, iii, and iv only C. iii and v only D. i, iii, and v only E. i, ii, and iv only 25. What are the initial elemental products formed at the anode and cathode if an aqueous solution containing 1M NaF (aq) is electrolyzed at 25 o C? Initial product at the ANODE Initial product at the CATHODE A. F 2 (g) Na (s) B. O 2 (g) Na (s) C. H 2 (g) O 2 (g) D. F 2 (g) H 2 (g) E. O 2 (g) H 2 (g) END OF EXAM

11 ANSWER KEY 1. E 2. A 3. C 4. E 5. C 6. C 7. D 8. C 9. A 10. A 11. D 12. A 13. D 14. B 15. A 16. D 17. B 18. C 19. C 20. E 21. C 22. D 23. E 24. B 25. E