Chemistry 1A, Fall 2009 Midterm Exam #2 October 13, 2009 (90 min, closed book) Name:__________________________________ SID:___________________________________ GSI Name:________________  The test consists of 6 short answer questions and 20 multiple choice questions.  Put your written answers in the boxes provided. Answers outside the boxes may not be considered in grading.  Write your name on every page of the exam. Question Page Points Score Multiple Choice (1-20) 2-5 78 Question 21 6 8 Question 22-23 7 9 Question 24 8 10 Question 25 9 5 Question 26 10 10 Total 120 Useful Equations and Constants: pH = - log[H3O+] pX = - log X X = 10-pX Kw = 1×10-14 Strong acids and bases: HCl LiOH HNO3 NaOH H2SO4 KOH HClO4 HBr HI Acid dissociation constants (Ka) CH3COOH 1.75×10-5 NH4+ 5.70×10-10 HCN 6.2×10-10 CH3NH3+ 2.3×10-11 H2CO3 4.45×10-7 (CH3)3NH+ 1.58×10-10Name_____________________GSI__________ Page 2 of 10 Multiple choice. Circle the BEST answer and bubble the choice on your scantron form. 1. How many moles of HCl must be added to 1 liter of water to make [OH-] = 10-9 M? A) 10-9 moles B) 10-5 moles C) 10-2 moles D) there is no OH- in HCl (aq) 2. What is the pH of a 0.020M HCl solution? A) 1.0 B) 0.020 C) 2.0 D) 1.7 3. What is the pH of a 1.00M formic acid (HCOOH) solution? Ka = 1.80×10-4 A) 0.013 B) 0.00 C) 1.9 D) 3.7 4. What is the solubility of the salt lead chloride, PbCl2? Ksp = 1.7× 10-5 A) 4.1×10-3M B) 4.3×10-6 M C) 1.7×10-5M D) 1.6×10-2 M 5. Which solution requires the largest volume of 0.10 M HCl to reach the equivalence point? A) 50 mL 1.0 M NH3 B) 200 mL 2.0 M NaCl C) 100 mL 0.25 M NaOH D) 100 mL 0.40 M NaOH 6. Which reaction is an oxidation-reduction reaction? A) 6FeCl2(aq) + K2Cr2O7(aq) +14HCl 6FeCl3(aq) + 2CrCl3(aq) + 2KCl(aq) +7H2O (l) B) AgNO3 (aq) + NaCl (aq) gCl (s) + NaNO3 (aq) C) CaCO3 (s)  CaO (s) + CO2 (g) D) SO3 (g) + H2O (l)  H2SO4 (aq) 7. The solid CaSO4 is dissolved in 1.0 L of water. The solution formed establishes an equilibrium with a large amount of solid CaSO4. If you add 10 mL water and examine the solution after 10 minutes________________. A) the concentration decreases B) the equilibrium constant increases C) the solubility remains the same D) the solubility decreasesName_____________________GSI__________ Page 3 of 10 8. The diagrams shown below represent the concentration of reactants and products over time. Which of the graphs represent systems that have reached equilibrium? Why? Represents reactants Represents products A) B) C) D) A) Graph A because the concentrations are equal B) Graph B because the concentrations are constant C) Graph C because the concentrations are constant D) Graph D because the concentrations are constant 9. What conclusion can you draw from the data in the table? Ksp pH of saturated solution Mg(OH)2 2.0 x 10-13 ~10 Ba(OH)2 2.6 x 10-4 ~13 x A) Mg(OH)2 is not an electrolyte. B) Mg(OH)2 is more soluble than Ba(OH)2. C) Both Mg(OH)2 and Ba(OH)2 are completely dissociated into ions in solution. D) Molecules of Mg(OH)2 in solution are only partially dissociated. E) Mg(OH)2 is a weak base. 10. Equal moles of nitric acid, HNO3, and sodium hydroxide, NaOH are mixed. HNO3 (aq) + NaOH (aq)  NaNO3 (aq) + H2O (l) What happens to the equilibrium concentrations if you add solid sodium nitrate, NaNO3 (s), to the solution? A) The reaction proceeds to form more products. B) The pH increases above 7. C) The pH remains at 7. D) There is less water in the solution. E) The density of the solution increases. 11. Which compound will form a solution with the lowest pH? (Data is on page 1) A) NH4Cl B) Na2CO3C) N(CH3)3D) NaBr E) CH3COONa concentration time 0 0 concentration time 0 0 concentration time 0 0 concentration time 0 0Name_____________________GSI__________ Page 4 of 10 12. Which of the substances listed below is the strongest acid? A) B) C) D) E) 13. An aqueous solution of 1 mole of NaOH (sodium hydroxide) was added to an aqueous solution of 1 mole of CH3COOH (acetic acid). Which of the following statements is true about the solution? A) It contains more H3O+ions that OHionsB) It contains fewer H3O+ions than OHionsC) It contains as many H3O+ ions as OH ions D) It contains neither H3O+ions nor OHionsE) It contains as many CH3COOions as Na+ions 14. A 0.10 M solution of congo red indicator changes color from the blue-violet HIn molecule to the red In ion at a pH of 4. What is the equilibrium constant for the dissociation of congo red? A) 0.10 B) 0.00010 C) 10000 D) 4 E) 3.16×10-3 15. An equilibrium mixture of gases consists of [CO] = 2.5×10-3 M, [O2] =1.6×10-3 M, and [CO2] = 3.2×10-2 M. Determine the equilibrium constant for the formation of CO2. A) 8.0×103 B) 1.0×105 C) 1.3×10-7 D) 1.3×10-4 E) 1.0 x 10-5 16. Equal moles of HCl, CH3COOH, and NH3 are mixed in water. What are the three species in solution present in the highest concentrations? A) HCl, CH3COOH, and NH3 B) H+, CH3COO-, and NH4+C) H+, NH3, and CH3COOH D) H+, Cl-, and NH4+ E) Cl-, NH4+, and CH3COOHName_____________________GSI__________ Page 5 of 10 17. The illustration shows an equilibrium mixture for the reaction of A2 and B2. A2 (g) + B2 (g)  2AB (g) How can you produce this equilibrium mixture? A) Mix 4 molecules of A2 and 4 molecules of B2 and allow them to react. B) Mix 6 molecules of A2 and 6 molecules of B2 and allow them to react. C) Begin with 6 molecules of AB and allow some to decompose. D) Begin with 8 molecules of AB and allow some to decompose. E) Both (A) and (D) 18. Silver chloride, AgCl, is less soluble than silver bromide, AgBr. Do you expect silver cyanide, AgI, to be more or less soluble than AgBr? A) AgI is more soluble than AgBr because the trend is dominated by the decrease in lattice energy. B) AgI is more soluble than AgBr because the trend is dominated by the increase in lattice energy. C) AgI is less soluble than AgBr because the trend is dominated by the decrease in hydration energy. D) AgI is less soluble than AgBr because the trend is dominated by the increase in hydration energy. E) AgI is more soluble than AgBr because Iis a stronger base than Br.