Test 2 first letter of last name --> Chemistry 12 Dr. Kline October 25, 2007 Name This test consists of a combination of multiple choice and other questions. There should be a total of 21 questions on six pages; please check to make sure that they are all here. The last page is an information sheet that may be removed. Do not use your own tables, scratch paper or other information. Please turn off all cell phones, pagers and other communication devices; they will be confiscated if they make noise. No food. No water. No gum. The test will end at 6 p.m. Multiple Choice Questions These 15 questions are worth three points each, for a total of 45 points. Unless it is stated otherwise in a given problem, there is only one correct answer for each question. Answer each question by circling all letter(s) corresponding to the correct choice(s); in other words, if more than one answer is correct, you should circle all of the correct ones. It is not necessary to show work for these questions; however, you may write on the exam. 1. Which of the following solutions has the highest poh? a.one with ph 8.21 b. one with [H + ]=4.0x10-9 M c. one with [OH - ]=2.0x10-6 M 2. Which of the following 0.10 M solutions would be acidic? More than one answer may be correct. a. LiBrO3 b. Fe(NO3)3 c. NH4F d. none 3. Which of the following 0.10M solutions would be basic? More than one answer may be correct. a. LiClO4 b. KHSO3 c. NaCN d. none 4. An unknown salt is one of the following listed below. A 0.10 M aqueous solution of the salt has ph 8.09. What is the identity of the salt? a. KCl b. KF c. NH4Cl d. KClO e. KHSO4 f. it is impossible to tell 5. In the reaction Ag + (aq) + 2 NH3(aq) Ag(NH3)2(aq) which substance is acting as the Lewis base? a. Ag + b. NH3 c. neither because this is not a Lewis acid-base reaction 6. Which of the following statements is/are true? More than one answer may be correct. a. the ph of a solution cannot be negative b. for an aqueous neutral solution at 35 C, ph=poh c. a 6 M aqueous NaOH solution contains no H + (or H3O + ) ions d. none of them 7. What is the ph of 1.000x10-8 M KOH at 25 C? a. 8.0000 b. 7.0000 c. 6.0000 d. 7.0217 e. 6.9783 Page 1 of 5 Test 2A Chem 12 (Fall 2007)
8. Which of the statements below concerning the aqueous reaction below is correct? More than one statement may be correct. Reaction: HCO3 - + HSO3 - H2CO3 + SO3 2- a. HCO3 - is acting as the acid b. SO3 2- is acting as the conjugate base c. K>1 for the reaction as written d. none of the statements is correct 9. Suppose that 100. ml of 0.20M HClO is combined with 200. ml of 0.20 M NaClO. Which of the following is true of the resulting solution? a. ph = 7.53 b. ph < 7.53 c. ph > 7.53 10. Which of the following titrations will have its equivalence point at the highest ph? a. HBrO titrated with NaOH b. HClO titrated with NaOH c. HCl titrated with NaOH. d. it is impossible to tell 11. Which of the following is/are buffer solutions? More than one answer may be correct. a. 100. ml each of 0.20 M HBrO and 0.10 M KOH b. 100. ml each of 0.10 M KBrO and 0.10 M HCl c. 100 ml of 0.10 M KBrO and 75 ml of 0.10 M HCl d. none of them 12. Which of the following would make a suitable buffer for approximately ph 3? More than one answer may be correct. a. mixture of 0.10 M HNO2 with excess 0.10 M NaOH b. mixture of 0.10 M NaOH with excess 0.10 M HNO2 c. mixture of 0.10 M HCl with excess 0.10 M KNO2 d. none of these 13. Which of the following saturated solutions has the greatest concentration of copper (II) ions at equilibrium? a. CuC2O4 b. CuS c. Cu(OH)2 14. In which of the following would Ni(OH)2 be the most soluble? a. deionized water b. 0.20 M Ni(NO3)2 c. 0.10 M KOH d. 0.10 M HCl 15. Is a precipitate expected to form when 50. ml of 0.10M Pb(NO3)2 is combined with 100 ml of 0.20 M HCl and 200. ml of deionized water? a. yes b. no c. it is impossible to tell Page 2 of 5 Test 2A Chem 12 (Fall 2007)
Other Questions Each of the following questions is worth the indicated number of points, for a total of 55 points. Please be sure to provide all of the information requested for each question. Please show work with units in order to receive credit for questions 18-21. 16. 8 points Arrange the following eight 0.10 M aqueous solutions of the following in order from lowest to highest ph. No work is necessary. LiBr HBrO2 KBrO3 LiOH HClO4 KBrO H2SO4 KClO3 < < < < < < < lowest ph highest ph 17. 10 points Circle the substance with the indicated property in each part. a. stronger acid: H2SO3 HIO3 b. stronger base: Se 2- S 2- c. greater molar solubility: PbCl2 Hg2Cl2 d. higher ph: 0.010 M HNO2 0.10 M HNO2 e. weaker acid: HBrO2 HIO2 18. 6 points Calculate the value of Kb for HPO4 2-. Show work. 19. 11 points How many ml of 0.250 M HCl must be added to 250. ml of 0.125 M NaBrO2 in order to make a buffer at ph 8.50? Show work. 20. 11 points Suppose that the following aqueous solutions are combined: 150. ml of 0.400 M silver nitrate and 200. ml of 0.300 M potassium oxalate. A precipitate of silver oxalate is formed by the balanced molecular equation written below. Calculate the concentrations of silver ion and oxalate ion remaining in solution. Show work. 2AgNO3(aq) + K2C2O4(aq) Ag2C2O4(s) + 2KNO3(aq) 21. 11 points Suppose that 25.00 ml of an aqueous solution of HNO2 is titrated with 0.1123 M NaOH and that 28.92 ml of the NaOH solution are required to reach the equivalence point of the titration. Calculate a-the concentration of the original HNO2 solution and b-the ph of the titrated solution at the equivalence point. Page 3 of 5 Test 2A Chem 12 (Fall 2007)
TEST #2 Information You may (carefully) remove this sheet from the test. Quadratic Equation For an equation of the type ax 2 + bx + c = 0 x = b ± b2 4ac 2a Acids, Bases and Buffers ph = -log(h + ) poh = -log(oh - ) Kw = (H + )(OH - ) pkw = ph + poh Kw = 1.0 x 10-14 at 25 C pkw = 14.00 at 25 C For a weak acid and its conjugate base, KaxKb=Kw pka = -logka ph = pka + log na nha poh = pkb + log nha na Ionization Constants of Acids at 25 C Acid HA A Ka pka Ammonium ion NH4 + NH3 5.6 10 10 9.25 Bromous HBrO2 BrO2-2.00x10-9 8.7 Carbonic (1) H2CO3 HCO3 4.3 10 7 6.37 Carbonic (2) HCO3 CO3 2 4.8 10 11 10.32 Hydrocyanic HCN CN 6.17 10 10 9.21 Hydrofluoric HF F 6.6 10 4 3.18 Hypochlorous HClO ClO 3.0 10 8 7.53 Nitrous HNO2 NO2 4.6 10 4 3.34 Oxalic (1) H2C2O4 HC2O4 5.9 10 2 1.23 Oxalic (2) HC2O4 C2O4 2 6.4 10 5 4.19 Phosphoric (1) H3PO4 H2PO4 7.52 10 3 2.12 Phosphoric (2) H2PO4 HPO4 2 6.23 10 8 7.21 Phosphoric (3) HPO4 2 PO4 3 2.2 10 13 12.67 Sulfuric (1) H2SO4 HSO4 ~10 2 ~ 2 Sulfuric (2) HSO4 SO4 2 1.2 10 2 1.92 Sulfurous (1) H2SO3 HSO3 1.54 10 2 1.81 Sulfurous (2) HSO3 SO3 2 1.02 10 7 6.91 Page 4 of 5 Test 2A Chem 12 (Fall 2007)
Solubility Product Constants at 25 C Ionic Solid Ksp Ag2C2O4 5.40x10-12 Cu(OH)2 4.8x10-20 CuC2O4 4.43x10-10 CuS 8x10-37 Ni(OH)2 5.48x10-16 PbCl2 1.70x10-5 Hg2Cl2 1.43x10-18 Page 5 of 5 Test 2A Chem 12 (Fall 2007)