Cheat Sheet and Final Exam for Majors Analytical Chemistry | CHEM 2154, Exams of Analytical Chemistry

Download Cheat Sheet and Final Exam for Majors Analytical Chemistry | CHEM 2154 and more Exams Analytical Chemistry in PDF only on Docsity! CHEM 2154 - Analytical Chemistry Exam II Fall 2009 Student Number: Print Name: Honor Code Statement: As stated on the syllabus, the Virginia Tech Undergraduate Student Honor Code applies to all work and exams in this course. By signing here, you certify that you neither gave nor received aid on any part of this exam. Honor Code Pledge: Constants and conversion factors: R = 8.314 J/(K•mol), 0.08206 L•atm/ (mol•K) F (Faraday constant) = 96,485 C/mol = 96,485 J/mol·V 1 atm = 760 Torr = 760 mm Hg = 14.7 psi=1.01x105Nm-2 Avogadro’s number = 6.0221x1023 mol-1 Equations µ = 1/2 Σi zi2Ci , log γx = –[0.51z2(µ)1/2]/[1+(αx(µ)1/2/305)], quadratic equation: x = -[b±(b2 – 4ac)1/2]/2a, Henderson-Hasselbalch: pH = pKa + log([A-]/[HA]) or: pH = pKa (for BH+) + log[B]/[BH+] error for addition or subtraction: ei = (e12 + e22 + e32 + ...ei2)1/2 error for multiplication or division: %ei = (%e12 + %e22 + %e32 + ... %ei2)1/2 half reaction reduction potentials Eo (V) pH αY4- F2 (g) + 2e- → 2F-(aq) 2.87 1.0 7.52 X 10-18 Ce4+(aq) + e- → Ce3+(aq) 1.70 2.0 3.71 X 10-14 Au3+(aq) + 3e- → Au(s) 1.52 3.0 2.51 X 10-11 Cl2 (aq) + 2e- → 2Cl-(aq) 1.396 4.0 3.61 X 10-9 Cr2O72- (aq) + 14H+(aq) + 6e- → 2Cr3+(aq) + 7H2O(l) 1.33 5.0 3.54 X 10-7 O2 (g) + 4H+(aq) + e- → 2H2O(l) 1.229 6.0 2.25 X 10-5 Br2 (aq) + 2e- → 2Br-(aq) 1.087 7.0 4.80 X 10-4 NO3- + 4H+(aq) + 3e- → NO(g) + 2H2O(l) 0.964 8.0 5.39 X 10-3 Ag+(aq) + e- → Ag(s) 0.799 9.0 5.21 X 10-2 Fe3+(aq) + e- → Fe2+ 0.767 10.0 0.35 I2 (g) + 2e- → 2I-(aq) 0.536 Cu2+(aq) + 2e- → Cu(s) 0.337 AgCl(s) + e- → Ag(s) + Cl- 0.222 Sn4+(aq) + 2e- → Sn2+(aq) 0.139 2H+(aq) + 2e- → H2(g) 0.000 Sn2+(aq) + 2e- → Sn(s) -0.138 Ni2+(aq) + 2e- → Ni(s) -0.236 Fe2+(aq) + 2e- → Fe(s) -0.440 Cd2+(aq) + 2e- → Cd(s) -0.402 Zn2+(aq) + 2e- → Zn(s) -0.763 Cr2+(aq) + 2e- → Cr(s) -0.890 Standard Calomel Electrode 0.241 Standard Ag/AgCl Electrode 0.197 CHEM 2154 - Analytical Chemistry Exam II Fall 2009 Multiple choice: each problem is worth 5 points. 1. The term "effective" or "conditional" formation constant in EDTA complexation reactions, αY4-Kf, is used instead of Kf because: (circle one) (a) EDTA is present in solution in many forms and αY4-Kf treats the un-complexed EDTA all as one form (b) The αY4- factor takes the activity of the ions into account (c) αY4-Kf corrects the equilibrium constant for titration error in the measurement (d) True equilibrium in EDTA reactions is never established (e) The conjugate base for EDTA in solution interferes in the titration and αY4- corrects for the offset 2. For systems in which the metal ion reacts very slowly with EDTA, the direct titration reaction may not be appropriate for the analysis. In this case, which type of titration can be used? (a) Back titration (b) Displacement titration (c) Indirect titration (d) Masking titration (e) A metal ion indicator must be used 3. Given that Kf of CuY2- = 6.3 X 1018 and Kf of MgY2- = 6.2 X 108, calculate the equilibrium constant for the reaction Cu2+ + MgY2-  Mg2+ + CuY2-: (a) 6.3 X 1018 (b) l.0 X 1010 (c) 2.1 (d) 9.8 X 10-11 (e) 3.9 X 1027 4. Given that the equilibrium constant for the reaction: Ni2+ + Y4-  NiY2-, is 4.20 X 1018, what is the conditional formation constant for the reaction Ni2+ + EDTA  NiY2-, at a pH of 3.0? (a) 2.55 X 10-11 (b) 1.05 X 108 (c) 1.05 X 10-8 (d) 4.2 X 1018 (e) 3.92 X 1010 5. Calculate the concentration of Ni2+ in a solution that was prepared by mixing 50.0 mL of 0.0300 M Ni2+ with 50.00 mL of 0.0500 M EDTA. The mixture was buffered to a pH of 3.0. (Note the information from the previous problem) (a) 3.57 X 10-19 M (b) 0.0100 M (c) 0.0150 M (d) 1.43 X 10-8 M (e) 7.00 X 107 M