8. Relax and do well.

Transcription

1 CHEM 1515 Name Exam III TA's Name John III. Gelder April 7, 1993 Lab Section INSTRUCTIONS: 1. This examination consists of a total of 8 different pages. The last 2 pages include important mathematical equations and constants, a solubility table, a periodic table, and a table of dissociation constants. All work should be done in this booklet. You may carefully remove the last 2 pages of the examination. 2. PRINT your name, your TA's name and your laboratory section now in the space at the top of this sheet. DO NOT SEPARATE THE PAGES. 3. Answer all questions that you can and whenever called for show your work clearly. Your method of solving problems should pattern the approach used in lecture. You do not have to show your work for the multiple choice or short answer questions. 4. No credit will be awarded if your work is not shown in problems 2 4. Please circle your final answer! 5. Point values are shown next to the problem number. 6. Budget your time for each of the questions. Some problems may have a low point value yet be very challenging. If you do not recognize the solution to a question quickly, skip it, and return to the question after completing the easier problems. 7. Look through the exam before beginning; plan your work; then begin. 8. Relax and do well. Page 2 Page 3 Page 4 Page 5 TOTAL SCORES (29) (30) (20) (21) (100)

2 CHEM 1515 Exam III 2 (9) 1. Complete and balance the following reactions. Identify all product's phases as either (g)as, (l)iquid, (s)olid or (aq)ueous. Products which are soluble ionic compounds must be written as ions. If no reaction occurs, write NR. a) KHC 8 H 4 O 4 (aq) + KOH(aq) b) Cu(NO 3 ) 2 (aq) + KIO 3 (aq) c) C 5 H 5 N(aq) + HC 2 H 3 O 2 (aq) (10) 2. Calculate the ph of an aqueous solution which is M (CH 3 ) 3 N. (10) 3. Calculate the ph of an aqueous solution formed after mixing 40.0 ml of M KOH and 30.0 ml of M HC 4 H 7 O 2.

3 CHEM 1515 Exam III 3 (30)4a. Calculate the ph of 500. ml of an aqueous solution which is M HC 7 H 5 O 2 (benzoic acid). b. Calculate the ph of the 500. ml solution in part a) after adding moles of KC 7 H 5 O 2. (Assume no volume change.) c. Briefly explain why the ph of the solution in part b) differs from the ph of the solution in part a). d. Calculate the ph of the 500. ml solution in part b) after adding moles of HNO 3. (Assume no volume change.)

4 CHEM 1515 Exam III 4 (20) 5. The formula for acetic acid, HC 2 H 3 O 2, which we use in class can also be written as CH 3 COOH. a) draw the Lewis structure for acetic acid. b) write the chemical equation which describes how acetic acid acts as an acid. c) write the definition of a Br/o nsted-lowry acid d) using the Lewis structure in part a) identify the acidic hydrogen in acetic acid. e) write the formula for, and draw the Lewis structure for the conjugate base of acetic acid f) write the definiton for a Br/o nsted-lowry base. g) trichloroacetic acid has the formula HC 2 Cl 3 O 2. Draw a Lewis structure for trichloroacetic acid. Would you predict trichloroacetic acid to be a stronger acid compared to acetic acid, weaker or about the same in strength? Provide a brief explanation to support your answer.

5 CHEM 1515 Exam III 5 Multiple Choice: (14 points) Print the letter (A, B, C, D, E) which corresponds to the answer selected ONLY THE ANSWERS IN THE AREA ABOVE WILL BE GRADED. Select the most correct answer for each question. Each question is worth 3 points. 6. Which of the following buffer systems would be the best to use if you needed to prepare a buffer with nearly equal amounts of the acid and conjugate base and having a ph = 7.40, the same ph as blood? A) H 3 PO 4 /H 2 PO 4 B) HC 2 H 3 O 2 /C 2 H 3 O 2 C) H 2 PO 4 /HPO 4 2 D) NH 4 + /NH 3 E) H 2 CO 3 /HCO 3 7. Which of the following is the strongest base? A) M C 6 H 5 NH 2 B) M KCN C) M HSO 4 D) M NH 3 E) M C 2 H 5 NH Calculate the magnitude of the equilibrium constant for the following reaction A) 1.0 x B) 6.4 x C) 4.9 x 10 4 D) 3.14 x 10 1 HCN(aq) + C 2 H 5 NH 2 (aq) C 2 H 5 NH 3 + (aq + CN (aq) 9. Which of the following salts gives an acidic solution? A) CH 3 NH 3 ClO 4 B) NaCl C) K 2 CO 3 D) KC 2 H 3 O 2 E) CaS 10. Calculate the initial concentration of a sample of acetic acid if the ph of the solution is A) 4.85 M B) M C) 1.1 x 10-5 M D) 1.4 x 10-5 M E) 2.5 x 10-5 M

6 CHEM 1515 Exam III A solution is labeled M H 2 CO 3, A) [H + ] less than M B) [CO 3 2 ] = M C) [H + ] = M D) [HCO 3 ] = M E) [H + ] = M 12. The ph of a 3.50 x 10 3 M Ca(OH) 2 solution is, A) 2.15 B) 2.46 C) D) E) can not determine the ph of the solution without a value for K b.

7 CHEM 1515 Exam III 7 Equations ph = log[h + ] x 1,2 = b± b2 4ac 2a ph + poh = 14 Solubility Table Useful Information Constants for ax 2 + bx + c = 0 K w = 1.0 x Ion Solubility Exceptions NO 3 soluble none ClO 4 soluble except NH + 4 Cl soluble except Ag +, Hg 2+ 2, *Pb 2+ SO 2 4 soluble except Ca 2+, Ba 2+, Sr 2+, Hg 2+, Pb 2+, Ag + CO 2 3 insoluble except Group IA and NH + 4 PO 3 4 insoluble except Group IA and NH + 4 OH insoluble except Group IA, *Ca 2+, Ba 2+, Sr 2+ S 2 insoluble except Group IA, IIA and NH + 4 Na + soluble none NH + 4 soluble except ClO 4 K + soluble none *slightly soluble

8 CHEM 1515 Exam III IA 1 H IIA 4 Li Be Na Mg K Ca Rb Sr Cs Ba Fr (223) Ra IIIA IVA VA VIA VIIA B C N O F 9 10 Ne IIIB IVB VB VIB VIIB VIII IB IIB Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Y Zr Nb Mo Tc Ru Rh Pd A g Cd In Sn Sb Te I Xe (98) La Periodic Table of the Elements Hf Al Si P S Cl VIIIA 2 Ta W Re 75 Os Ir Pt Au Hg 80 Tl Pb Bi Po At Rn (209) (210) 89 Ac (261) (262) (263) He Ar (222) Lanthanides Actinides Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu (145) Th Pa U Np Pu AmCm Bk Cf Es Fm Md No Lr (244) (243) (247) (247) (251) (252) (257) (258) (259) (260)

9 CHEM 1515 Exam III 9 E.1 DISSOCIATION CONSTANTS FOR ACIDS AT 25 C Name Formula K a1 K a2 K a3 Acetic HC 2 H 3 O x 10 5 Ascorbic HC 6 H 7 O x 10 3 Arsenic H 3 AsO x x x Arsenous H 3 AsO x Benzoic HC 7 H 5 O x 10 5 Boric H 3 BO x Butyric acid HC 4 H 7 O x 10 5 Carbonic H 2 CO x x Cyanic HCNO 3.5 x 10 4 Citric H 3 C 6 H 5 O x x x 10 7 Formic HCHO x 10 4 Hydroazoic HN x 10 5 Hydrocyanic HCN 4.9 x Hydrofluoric HF 7.2 x 10 4 Hydrogen chromate ion HCrO x 10 7 Hydrogen peroxide H 2 O x Hydrogen selenate ion HSeO x 10 2 Hydrogen sulfate ion HSO x 10 2 Hydrogen sulfide H 2 S 5.7 x x Hypobromous HBrO 2.0 x 10 9 Hypochlorous HClO 3.0 x 10 8 Hypoiodus HIO 2.0 x Iodic HIO x 10 1 Lactic HC 3 H 5 O x 10 4 Malonic H 2 C 3 H 2 O x x 10 6 Oxalic H 2 C 2 O x x 10 5 Nitrous HNO x 10 4 Phenol HC 6 H 5 O 1.3 x Phosphoric H 3 PO x x x Paraperiodic H 5 IO x x 10 9 Propanoic HC 3 H 5 O x 10 5 Pyrophosphoric H 4 P 2 O 3.0 x x 10 3 Selenous H 2 SeO x x 10 9 Sulfuric H 2 SO 4 strong acid 1.2 x 10 2 Sulfurous H 2 SO x x 10 8 Tartaric H 2 C 4 H 4 O x x 10 5 E.2 DISSOCIATION CONSTANTS FOR BASES AT 25 C Name Formula K b Name Formula K b Ammonia NH x 10 5 Hydroxylamine HONH x 10 8 Aniline C 6 H 5 NH x Methylamine CH 3 NH x 10 4 Dimethylamine (CH 3 ) 2 NH 5.4 x 10 4 Pyridine C 5 H 5 N 1.7 x 10 9 Ethylamine C 2 H 5 NH x 10 4 Trimethylamine (CH 3 ) 3 N 6.4 x 10 5 Hydrazine H 2 NNH x 10 6