Test 1 first letter of last name Chemistry 12 Dr. Kline 26 October 2005 Name This test consists of a combination of multiple choice and other questions. There should be a total of 24 questions on 8 pages; please check to make sure that they are all here. You may use the equation/information sheet and any periodic table provided (on page 9). Do not use your own tables, scratch paper or other information. Do not share your calculator. Please turn off all cell phones, pagers and other communication devices; if they make noise, they will be confiscated. Shared calculators will be confiscated. Multiple Choice Questions Each of the following 19 questions is worth three points, for a total of 57 points. It is not necessary to show work for these questions; however, you may write on the exam. Answer each question by circling the letter(s) corresponding to the correct choice(s). Unless it is stated otherwise in a given problem, there is only one correct answer for each question. In questions where it states that more than one answer is possible, there may be one or more correct answers: please circle all of the correct answers. 1. Which of the following corresponds to the most basic solution? a. [H + ] = 5.0x10-9 M b. [OH - ] = 5.0x10-4 M c. ph = 9.25 d. poh = 5.50 2. Which of the following compounds produce a basic solution when dissolved in water (assume water has a ph = 7). More than one answer may be correct. a. Na 2 SO 4 b. Ba(NO 3 ) 2 c. AlBr 3 d. none 3. Is the compound NH 4 CN acidic, basic, or neutral? a. acidic b. basic c. neutral 4. Which of the following net ionic equations accounts for the acid-base behavior of the compound in question #3? a. NH 4 + (aq) NH 3 (aq) + H + (aq) b. NH 3 (aq) + H 2 O(l) NH 4 + (aq) + HO - (aq) c. HCN(aq) CN - (aq) + H + (aq) d. CN - (aq) + H 2 O(l) HCN(aq) + HO - (aq) e. none of them because the compound is neutral 5. Which compound is acting as the Lewis acid in the reaction Ag + + 2 NH 3 Ag(NH 3 ) 2 +? a. Ag + b. NH 3 c. neither, because it s not a Lewis acid-base reaction Page 1 of 1 Test 2C Intenet Chem 12
6. Into which category of acid-base reaction is the reaction F - (aq) + HSO 4 - (aq) HF(aq) + SO 4 2- (aq) classified? More than one answer may be correct. a. Bronsted-Lowry b. Arrhenius c. Lewis d. none, because it s not an acid-base reaction 7. Which of the following solutions has the highest concentration of fluoride ions? a. 0.10 M HF b. 0.10 M HF with 0.10 M HCl c. 0.20 M HF d. 0.20 M HF with 0.10 M HCl e. There is a tie among two or more of the above choices. 8. An aqueous solution is 1.000x10-8 M in HI. Which of the following is true concerning the ph of the solution? a. ph = 7.0000 b. ph = 8.0000 c. ph = 6.000 d. 6.0000 < ph < 7.0000 e. 7.0000 < ph < 8.0000 9. In which of the following are the two species correctly arranged so that the acid predicted to be the stronger acid is listed first? More than one choice may be correct. a. H 2 PO 4 > H 3 PO 4 b. NH 3 > PH 3 c. H 3 PO 4 > H 2 SiO 3 d. none 10. What is true of K for the reaction HIO 2 + BrO - IO 2 - + HBrO that occurs in aqueous solution? a. K = 1 b. K < 1 c. K > 1 d. it is impossible to tell 11. Suppose that the triprotic acid H 3 Z has K a1 = 4.0x10-3, K a2 = 2.0x10-8, and K a3 = 5.0x10-12. What is the value of K for the reaction H 2 Z - (aq) + H 2 O(l) OH - (aq) + H 3 Z? a. 2.5x10 2 b. 5.0x10 7 c. 2.0x10 11 d. 2.5x10-12 e. 5.0x10-7 f. 2.0x10-3 Page 2 of 2 Test 2C Intenet Chem 12
12. Which of the following is/are buffer solutions? More than one answer may be correct. a. 50. ml of 0.10 M HClO plus 25 ml of 0.20 M NaOH b. 50. ml of 0.10 M HCl plus 20. ml of 0.10 M NaClO c. 50. ml of 0.10 M HClO plus 20. ml of 0.10 M NaOH d. none of them 13. Which of the following aqueous solutions has the highest ph? a. 100. ml of 0.100 M HBrO plus 100. ml of 0.200 M KBrO b. 100. ml of 0.100 M HBrO plus 100. ml of 0.250 M KBrO c. 100. ml of 0.200 M HBrO plus 100. ml of 0.200 M KBrO d. all of them have the same ph because they contain the same acid-conjugate base pair e. it is impossible to tell without the K a of HBrO or the K b of BrO - 14. Suppose that each of the following 0.1000 M aqueous acids is titrated with 0.1000 M NaOH. Which will have the lowest ph at the equivalence point? a. HBrO 2 b. HClO 2 c. HIO d. HBrO e. it is impossible to tell 15. Which of the following statements is true regarding the titration of a weak base (in Erlenmeyer flask) with HCl (in buret)? More than one choice may be correct. a. at the equivalence point, ph > 7 b. the ph of the solution in the flask will decrease as the titration progresses c. the ph at the half-equivalence point can be acid, basic, or neutral, depending on the weak base used d. none of them 16. Which of the following indicators would be the most suitable for the titration of 0.1000 M CH 3 NH 2 (Erlenmeyer flask) with 0.1000 M HCl (buret)? Note: use the diagram below to select the indicator. This diagram is similar to the one in the lab book. a. Picophthalein b. SMC blue c. Corsair red ph Scale Indicator 0 2 4 6 8 10 12 14 Corsair red red yellow SMC blue blue yellow Picophthalein yellow red Page 3 of 3 Test 2C Intenet Chem 12
17. Which of the following has the greatest molar solubility? a. Mn(OH) 2 b. Ag 2 CrO 4 c. BaSO 4 d. Ag 3 PO 4 e. Cu(OH) 2 18. In which of the following aqueous solutions is BaCrO 4 the least soluble? a. plain deionized water b. 0.10 M HCl c. 0.10 M H 2 CrO 4 d. 0.20 M H 2 CrO 4 e. 0.20 M BaCl 2 f. it is impossible to tell 19. Suppose that three drops of 0.20 M KI are added to 100.0 ml of 0.0100 M Pb(NO 3 ) 2. Will a precipitate of PbI 2 form? Assume that one drop is 0.05 ml a. yes b. no Problems and Questions Each of the following is worth the indicated number of points, for a total of 43 points. Please show work with units to receive credit. Also, be sure to provide all of the information requested for each question. 20. 5 points Rank the following 0.10 M aqueous solutions in order of increasing ph using the blank lines near the bottom of this page. Please do not use arrows to adjust your answer. It is not necessary to show work for this question. NaOH HBrO LiI HClO 4 KBrO 2 KIO 2 HBrO 2 < < < < < < low ph high ph Page 4 of 4 Test 2C Intenet Chem 12
21. 10 points Consider the diprotic acid telluric acid, H 2 Te, that has K a1 = 2.3x10-3 and K a2 = 1.6x10-11. a. Write the reaction equations that correspond to K a1 and K a2. b. Calculate the total concentration of each aqueous species in your reaction equations that is present in a solution of 0.300 M telluric acid. c. Calculate the ph of 0.300 M aqueous telluric acid. 22. 8 points What volume of 0.200 M HCl is needed to combine with 125 ml of 0.150 M KNO 2 in order to produce a buffer with a ph of 3.25? 23. 10 points Consider the titration of 27.25 ml of 0.1555 M HCHO 2 with 0.1222 M NaOH. What is the ph at the equivalence point of this titration? 24. 10 points Suppose that 45.0 ml of 0.200 M HgNO 3 is combined with 25.0 ml of 0.100 M K 2 CO 3, resulting in a precipitate of Hg 2 CO 3. Calculate the concentrations of all non-spectator ions present in the reaction mixture at the end of the reaction. <note since mercury (I) is diatomic, the formula of the first reactant should have been Hg 2 (NO 3 ) 2, but I didn t catch this until I was grading them; we ll just pretend that this problem concerned a rare form of mercury (I) that s not diatomic and that happens to have the same Ksp as the normal one when combined with carbonate> 2 HgNO 3 (aq) + K 2 CO 3 (aq) Hg 2 CO 3 (s) + 2 KNO 3 (aq) Page 5 of 5 Test 2C Intenet Chem 12
TEST #2 Information Fall 2005 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 - ) K w = (H + )(OH - ) pk w = ph + poh K w = 1.0 x 10-14 at 25 C pk w = 14.00 at 25 C For a weak acid and its conjugate base, K a xk b =K w pk a = -logk a # & ph = pka + log na " # & % ( poh = pkb + log nha % ( $ nha ' $ na "' Dissociation Constants for Some Acids at 25 C (listed numerically by Ka) Name Formula K a Chromic acid H 2 CrO 4 K a1 = 0.18 K a2 = 3.2 x 10-7 Hydrogen sulfate ion HSO 4 1.1 x 10 2 Nitrous acid HNO 2 4.0 x 10-4 Formic acid HCHO 2 1.8 x 10-4 Acetic acid HC 2 H 3 O 2 1.8 x 10-5 Hydrocyanic acid HCN 6.2 x 10-10 Ammonium ion + NH 4 5.6 x 10-10 Hydrolysis Constants for Two Bases at 25 C (alphabetical order by name) Name Formula K b Ammonia NH 3 1.8 x 10-5 Methylamine CH 3 NH 2 4.4 x 10-4 Page 6 of 6 Test 2C Intenet Chem 12
Selected Solubility Product Constants at 25 C (listed alphabetically by formula) Name Formula K sp Silver chromate Ag 2 CrO 4 2.6 x 10-12 Silver phosphate Ag 3 PO 4 2.6 x 10-18 Barium chromate BaCrO 4 2.1 x 10-10 Barium sulfate BaSO 4 1.1 x 10-10 Copper (II) hydroxide Cu(OH) 2 2.2 x 10-20 Iron (III) hydroxide Fe(OH) 3 1.6 x 10-39 Lead (II) iodide PbI 2 7.9 x 10-9 Lead (II) iodate Pb(IO 3 ) 2 2.5 x 10-13 Manganese (II) hydroxide Mn(OH) 2 1.6 x 10-13 Mercury (I) carbonate Hg 2 CO 3 8.9 x 10-17 Page 7 of 7 Test 2C Intenet Chem 12