CHEM 7L PRACTICE EXAM #1

Transcription

1 CHEM 7L PRACTICE EXAM #1 IMPORTANT STUDY RECOMMENDATIONS In order to be best prepared for your upcoming midterm, which covers experiments 0-4A, make sure you review the following items: - Pre- and postlab questions - Lecture notes and exercises included in the lecture notes - Important lab calculations from your lab reports - Important background information and concepts covered in the lab manual - The practice exam provided in the next pages of this document (contains the answer key in addition to all the extra pages that would be provided in a normal exam). EXAM REVIEW SESSION(S) TBA by instructor/ta EXAM COURSE POLICIES Please review the exam course policies, including all exam dates in the course syllabus. As specified in the syllabus, several lab sections may be scheduled to take their exam in an overflow exam room (section assignment/location TBA by instructor/ta). Page 1 of 9

2 Please complete and sign CHEM 7L Practice Exam #1 FORM A University of California, San Diego I pledge that I have not used any unauthorized material on this exam. In addition, I have not provided anyone with unauthorized assistance. Full Name (printed) UCSD ID#: Name (signature) Lab Section # TA Name BEFORE THE START THE EXAM DIRECTIONS You must use a #2 lead pencil (not a pen!). Only materials allowed on your desk in addition to the exam materials provided by the instructor: pencils, erasers, a non-graphing, non-programmable calculator, your UCSD ID (required!!!!!!) SCANTRON INFO REQUIRED FOR YOUR TEST TO BE SCORED CORRECTLY: you must blacken the circle for "TEST FORM" A! Your test will not be rescored if you enter the wrong test form letter!!! SCANTRON INFO REQUIRED FOR YOUR TEST TO BE SCORED: Write your student ID # into the boxes below the "ID NUMBER" field with the last digit in the last box. Next, darken the bubbles in the corresponding ID fields. Note: "A" = "1 SCANTRON INFO REQUIRED: Write your Full Name and Lab Section # (in Hour/Day) DURING THE EXAM Use only SIDE 1 of the Scantron sheet. When you have selected your answer, blacken the corresponding space on the answer sheet Any question for which more than one response has been blackened (i.e. "overvoting") will not be counted AT THE END OF THE EXAM VERIFY THAT YOUR STATEMENT OF ACADEMIC INTEGRITY IS SIGNED (on top of this page) You will not be allowed to take your examination booklet with you when you leave the testing room. TURN IN YOUR SCANTRON AND THIS EXAM This exam is the property of the instructor. All rights reserved. DO NOT TURN THIS PAGE UNTIL YOU ARE INSTRUCTED TO DO SO!!!!!!!! KEEP YOUR EXAM COVERED AT ALL TIMES!!!!!! Page 2 of 9

3 CHEM 7L Practice Exam #1- Form A Name: (200 points) Section #: TA: Select the letter corresponding to the best answer for each question. Once you have selected your answer, blacken the corresponding space on your Scantron sheet. "Short" Questions (10 points): 1) Do the indicated arithmetic and give the answer the correct number of significant figures: ( ) = a) b) c) d) 51.6 e) ) A student collects 6 experimental data points: 31.2, 32.7, 27.9, 30.8, 33.2 and Using the Q-Test, determine the 'Q' value. Can the low value be discarded? a) 0.638, yes b) 1.21, yes c) 0.547, no d) 0.547, yes e) 0.638, no 3) In the gravimetric analysis of aluminum ion using 8-hydroxyquinoline as the precipitating agent, the experimenter should avoid: a) A large excess of the precipitating agent b) A low ph (less than 5 or so) c) A high ph (greater than 10 or so) d) All of the above e) None of the above 4) What is the proper relationship between pk a and ph at 1/4 the equivalence point? a) pk a = ph b) pk a = ph - log(1/3) c) pk a = ph - log(1/2) d) pk a = ph - log(2) e) pk a = ph - log(3) 5) In a coordination compound: a) The metal can simultaneously act as both a Lewis acid and a Lewis base b) The ligands act as the Lewis acids, the metal acts as the Lewis base c) The metal acts as the Lewis acid, the ligands act as the Lewis bases d) Either b or c is true, depending on the circumstances e) None of the above is true "Long" Questions (20 points): 6) Consider the experimental data sets obtained for the length of an object as measured by three students A, B, C in the laboratory. The length is known to be cm. Each student performed a total of five trials as presented in the table below. Which of the following conclusions summarizes the data? Page 3 of 9

4 Trial 1 (cm) Trial 2 (cm) Trial 3 (cm) Trial 4 (cm) Trial 5 (cm) Student A Student B Student C a) Student C has done the most precise work and student A has done the most accurate work b) Student B has done the most precise work and student A has done the most accurate work c) Student A has done the most precise work and student C has done the most accurate work d) Student C has done the most precise work and student B has done the most accurate work e) Student B has done the most precise work and student C has done the most accurate work 7) A sample of potassium chloride (KCl) that is contaminated with calcium chlorate (Ca(ClO 3 ) 2 ) is placed in a test tube. The KCl/Ca(ClO 3 ) 2 mixture in the tube is then heated, prompting the following reaction: _ Ca(ClO 3 ) 2 (s) + x KCl(s) _ CaCl 2 (s) + _ O 2 (g) + x KCl(s) During this experiment, the following data is collected: Mass of test tube = g Mass of KCl/Ca(ClO 3 ) 2 mixture + tube = g Mass of KCl/CaCl 2 residue + tube = g What are the weight % of Ca from the Ca(ClO 3 ) 2 impurity in the original mixture and the weight % of the KCl in the original mixture, reported to three significant figures? Molar masses: Ca 2+ : g/mol; ClO 2-3 : g/mol; K + : g/mol; Cl - : g/mol; O 2 : g/mol a) 5.89% and 69.6% b) 17.7% and 91.3% c) 1.96% and 89.9% d) 5.89% and 30.4% e) 1.96% and 10.1% 8) A 78.0 ml solution of highly concentrated Ca(NO 3 ) 2 is added to 109 ml of a solution of NaF of unknown concentration and g of a white powder precipitates out of solution. What is the original concentration of the NaF solution? Molar masses: Na + : g/mol; F - : g/mol; Ca 2+ : g/mol; NO - 3 : g/mol a) M b) M c) M d) M e) M 9) A solution is prepared by dissolving 7.75 mmol of CH 3 (CH 2 ) 6 CO 2 H (octanoic acid) in 125 ml of water. The ph of the resulting solution is measured to be From this information, what is the pk a of octanoic acid? a) 6.12 b) 1.84 c) 4.91 d) 4.01 e) ) Sulfuric acid (H 2 SO 4 ) can be formed according to the following reaction: _ SO 2 (g) + _ O 2 (g) + _ H 2 O (g) _ H 2 SO 4 (g) Page 4 of 9

5 If 400 g of SO 2, 175 g of O 2 and 125 g of H 2 O are reacted, what is the limiting reagent and how many grams of H 2 SO 4 are produced (assuming 100% yield)? Hint: Balance the reaction equation first! Molar masses: SO 2 : g/mol; O 2 : g/mol; H 2 O: g/mol; H 2 SO 4 : g/mol a) SO 2 and 306 g b) SO 2 and 612 g c) O 2 and 536 g d) H 2 O and 681 g e) O 2 and 1070 g Two-Part Questions Two-Part Question A: 11) Part I (20 points). A basic solution of Ca(OH) 2 is standardized versus g of KHP (potassium hydrogen phtalate) acid and the volume of Ca(OH) 2 needed to fully titrate this mass of KHP is ml. What is the standardized concentration of the Ca(OH) 2 solution? Molar masses: K + : g/mol; hydrogen phthalate (-): g/mol; Ca 2+ : g/mol; OH: g/mol a) M b) M c) M d) M e) M 12) Part II (10 points). Once standardized, a total of ml of the Ca(OH) 2 standard solution from question 11) is required to totally react with g of an unknown diprotic acid. Based on your calculations, the molar mass of the unknown acid appears to be closest to which of the following? a) Lithium formate (51.96 g/mol) b) Propylene glycol (76.10 g/mol) c) Succinic acid ( g/mol) d) Adipic acid ( g/mol) e) Tetrachloro-phthalic acid ( g/mol) Two-Part Question B: 13) Part I (10 points). A student synthesizes the following coordination compound in the laboratory: K[Fe(C 2 O 4 ) 2 ] 6H 2 O. What is the coordination number of the complex and the oxidation state of the metal in this complex? a) 4, 3+ b) 2, 3+ c) 4, 2+ d) 2, 2+ e) None of the above 14) Part II (10 points). Which of the following species is present in the outer sphere of the complex discussed in Question #13? 2- a) C 2 O 4 b) H 2 O c) K + d) b and c e) a and b The answer key to this practice midterm is provided on Page 9 Note: Pages 6-8 are provided with any regular 7L exam Page 5 of 9

6 Periodic Table of the Elements Page 6 of 9

7 SCRATCH PAPER: RETURN ALL SCRATCH PAPER WITH YOUR EXAM!!!!!!! Page 7 of 9

8 CHEM 7L COMMON FORMULAS & VALUES i 1 x - x N -1 i 2 outlier - value closest to outlier Q highest value - lowest value N = 3: QC = 0.94; N = 4: QC = 0.76 ; N = 5: QC = 0.64 ; N = 6: QC = 0.56 K a = [H + ][A ] [HB ][OH ] K b = [HA] [B] K w = K a K b = ph = -log[h + ] = 14 - poh pk a = -log[k a ] If A z B y z A + y B, then K sp = [A] z [B] y q = m c T = n C P T q cold = -q hot C metal 26 J/K mol c water = 4.18 J/K g C water = 75.3 J/K mol 100% 1 A = log = log = log %T T I % T = 100 T T = 10 1A I o Beer's law: c = E = h A = bc, where = molar absorptivity (in M -1 cm -1 ), b = cell length (usually 1.0 cm) and c = concentration (c = m/s) (h = J s) For hydrogen: E = E = kj mol 1 2 n f n i R H h N A = kj/mol (N A = molec./mol) Page 8 of 9

9 ANSWER KEY: 1) E 2) C 3) D 4) B 5) C 6) B 7) C 8) B 9) C 10) B 11) A 12) D 13) A 14) D Page 9 of 9