Fundamentals of Analytical Chemistry - Resolution of Practice Exam 1 | CHE 215.00, Exams of Analytical Chemistry

Download Fundamentals of Analytical Chemistry - Resolution of Practice Exam 1 | CHE 215.00 and more Exams Analytical Chemistry in PDF only on Docsity! 1 Chemistry 215 – Fundamentals of Analytical Chemistry Exam 1 February 4, 2004 75 POINTS Name KEY SEE EQUATIONS AND TABLES ON LAST PAGE PART I. DEFINITIONS (9 Points) Define the following terms as they relate to the topics covered in this course. 1. Analytical Chemistry (3 Points) Characterization of the composition of matter, usually involving quantitative and/or qualitative analysis. 2. Primary Standard (3 Points) A pure reagent that can be weighed directly to provide a known number of moles. 3. Confidence Interval (3 Points) The range of values within which the true mean is likely to fall with a certain probability. IMPORTANT NOTE BEGINNING NEXT MONDAY (FEBRUARY 9) OUR CLASS WILL MEET IN JULIAN 225 CHE 215 Exam 1 Feb. 4, 2004 2 PART II. CALCULATIONS (45 Points) Show all calculations in order to earn partial credit. 1. Municipal drinking water is often fluoridated in order to promote dental health. a. The target fluoride ion (F-) concentration is 1.0 ppm. What is this concentration in molarity, M? The atomic weight of F is 18.998 g/mol. (5 Points) Since 1.0 ppm = 1.0 mg/L, simply convert 1.0 mg to moles: −−×=                  F M 105.3 g 18.998 mol 1 mg 1000 g 1 L mg 1.0 5 b. How much sodium fluoride (NaF, MW = 41.99 g/mol) must be added to a 10,000- gallon tank (1 gallon = 3.785 L) so that the final concentration of F- is 1.0 ppm? Express your answer in g. (5 Points) Note: you weigh out NaF, not F-, so you can’t just go from 1.0 ppm F- to mass. Instead, use the concentration from part a, since [F-] = [NaF]. ( ) NaFg 84. mol NaFg 41.99 L NaF mol 105.3 gal L 3.785gal 10,000 -5 =              ×       CHE 215 Exam 1 Feb. 4, 2004 5 b. A 25.00-mL aliquot of KMnO4 required 34.43 mL of this Na2C2O4 solution to reach the endpoint. Calculate the concentration of the KMnO4 solution. (6 Points) First calculate the number of moles of C2O42-: ( ) mol 105.208 L mol 0.015127L 0.03443 4−×=      Next, calculate the number of moles of MnO4-: ( ) mol 102.083 OC mol 5 MnO mol 2mol 105.208 4-2 42 - 44- −×=       × Finally, calculate the concentration: M 0.008333 L 0.02500 mol 102.083 -4 =       × PART III. SHORT ANSWER (10 Points) ***ANSWER ONLY 2 OF THE FOLLOWING 3 QUESTIONS *** NOTE: If you answer all three questions, only the first two will be graded. 1. Explain what is meant by Formal concentration. (2½ Points) Formal Concentration is used to describe the overall concentration of an electrolyte in solution disregarding dissociation reactions. Therefore the formal concentration represents what was weighed out; molar concentration should represent what is actually present in solution. One mole of NaCl (58.55 g) was added to 1 liter of water. Is this solution 1 M NaCl, 1 F NaCl, or are both correct descriptions? Explain. (2½ Points) This should be expressed as 1 F NaCl because when NaCl is dissolved in water it completely dissociates, so [NaCl] = 0 M but [Na+] = [Cl-] = 1 M. CHE 215 Exam 1 Feb. 4, 2004 6 2. Complete the following table of SI units. (5 Points) SI Prefix Value 10-3 milli 103 kilo 106 mega 10-2 centi 10-12 pico 10-9 nano 10-15 femto 109 Giga 1012 Tera 10-1 deci 10-18 atto BONUS: Add up to 3 not listed above 3. Following are 5 common titration reactions. Categorize each reaction as a precipitation, complexation, acid-base, or redox titration. (5 Points) CH2(CO2H)2 + 2 H2O + 6 Ce4+ ⇌ 2 CO2 + HCO2H + 6 Ce3+ + 6 H+ REDOX Fe3+ + Y4- ⇌ FeY- (where Y = EDTA) COMPLEXATION 2 HCl + Na2CO3 ⇌ CO2 + 2 NaCl + H2O ACID-BASE MnO4- + 5 Fe2+ + 8 H+ ⇌ Mn2+ + 5 Fe3+ + 4 H2O REDOX Ag+ + SCN- ⇌ AgSCN (s) PRECIPITATION Example: CHE 215 Exam 1 Feb. 4, 2004 7 PART IV. MULTIPLE CHOICE (12 Points) Choose the BEST answer for the following questions. 1. A systematic error a. usually cannot be discovered and corrected. b. must be treated with statistics. c. is also known as determinate error. d. is also known as indeterminate error. 2. The accuracy of a measurement can best be assessed by a. analyzing a standard reference material. b. calculating the standard deviation of a replicate set of measurements. c. analyzing a blank. d. All of these answers are true. 3. What volume of a 100.0 ppm Cu solution would be required to make 1.00 L of a 2.00 ppm Cu solution? a. 50.0 mL b. 200. mL c. 2500 mL d. 20.0 mL e. None of these answers are correct. 4. The point in a titration where the quantity of titrant added is exactly that required to completely react with the analyte is called the a. end point. b. equivalence point. c. stoichiometry point. d. exclamation point. e. extra point. 5. A student wished to determine the concentration of chromium (Cr) in the wastewater stream of an automobile plant. After analyzing a series of standards, the student made a calibration curve and found that the best-fit line had the formula: Absorbance = 0.342[Cr in ppm] + 0.023 The student analyzed an unknown and found an absorbance of 0.430. What is the concentration of Cr in the unknown (in ppm)? a. 1.19 b. 0.170 c. 3.41 d. 7.11 e. None of these answers are correct. 6. Starting next Monday class meets in room a. Julian 225 b. Julian 225 c. Julian 225 d. Julian 225 e. All of the above