Chemistry Exam I - Fall 2014 for Chemistry 1055 - Prof. Gordon T. Yee, Exams of Chemistry

Download Chemistry Exam I - Fall 2014 for Chemistry 1055 - Prof. Gordon T. Yee and more Exams Chemistry in PDF only on Docsity! name _________________ Chemistry 1055 Hour Exam I Fall 2014 Dr. Gordon Yee Answer all questions on the computer-readable answer sheets by filling in the proper bubble with a No. 2 pencil. If you change an answer, erase the undesired mark thoroughly. Mark only the best answer to each question. Don’t forget that I have tried to write challenging, but not trick, questions. You may use a non- programmable calculator. Due to rounding, answers may differ by ±2 in the last significant figure. BE SURE TO FILL IN THE BOXES FOR YOUR STUDENT NUMBER AND NAME. THEN FILL IN THE CORRESPONDING BUBBLES BENEATH THE STUDENT NUMBER CORRECTLY. THE VERSION LETTER IS LOCATED ON THE LAST PAGE. THIS EXAM HAS 20 QUESTIONS, WORTH 5 POINTS EACH, ON 6 PAGES PLUS A PERIODIC TABLE. PLEASE CHECK TO SEE THAT YOU HAVE THEM ALL. SHOW YOUR WORK ON THE TEST BOOKLET. YOU HAVE 75 MINUTES. TURNING IN AN EXAMINATION IMPLIES THAT YOU AGREE TO ABIDE BY THE HONOR CODE. TURN IN YOUR WHOLE ANSWER BOOKLET. INSERT SOLUBILITY TABLE HERE name _________________ 1. Amphetamine is a central nervous system (CNS) stimulant and the active ingredient in Adderall. It contains only carbon, hydrogen and nitrogen and its molecular formula is C9H13N. What are the mass percent of carbon and hydrogen, respectively? a) C 79.95% H 9.69% f) C 89.21% H 11.20% b) C 65.21% H 9.26% g) C 76.01% H 18.21% c) C 86.01% H 5.01% h) C 84.00% H 18.21% d) C 74.00% H 5.01% i) C 89.42% H 4.16% e) C 69.42% H 11.20% j) C 95.21% H 4.16% 2. Which of the following samples contain the greatest number of potassium ions? a) 1 mol of KClO b) 1 mol of KClO2 c) 1 mol of KClO3 d) 1 mol of KClO4 e) all four samples contain the same number of potassium ions 3. The correct systematic name for SeO2 is a) selenium(IV) oxide b) selenium oxide c) selenium(IV) oxide (II) d) selenium dioxide e) sulfur(IV) oxide f) strontium peroxide 4. In lab, you reacted magnesium nitride with water to convert it to magnesium hydroxide and ammonia (NH3). If you balance this reaction with whole number coefficients having no common factor other than one, what are the coefficients on H2O and NH3, respectively? a) 2,6 b) 2,4 c) 6,2 d) 4,3 e) 4,4 f) 5,3 g) 3,6 h) none of these answers is correct name _________________ 12. A common isotope of an element in your body has 26 protons and 30 neutrons. Which of the following statements is true? a) There is not enough information to identify this element. b) This element has a mass number of 26. c) This element can exists in different compounds with variable positive charge. d) This element is a non-metal. e) This element has an atomic mass of exactly 56 amu by definition. 13. Propylene, C3H6, (42.08 g/mol) reacts with nitrogen monoxide to form acrylonitrile, C3H3N, (56.09 g/ mol) a component of the polymer that LEGO are made of. What amount of acrylonitrile can be produced from 2.84 g of propylene and 4.22 g of nitrogen monoxide? 4 C3H6 (g) + 6 NO (g) → 4 C3H3N (s) + 6 H2O (l) + N2 (g) a) 1.99 g b) 3.11 g c) 3.78 g d) 4.36 g e) 7.89 g f) 11.83 g 14. Regarding the question above, if you isolate 3.30 g of acrylonitrile, what is the percent yield? a) 58.4% b) 65.7% c) 72.1% d) 87.3% e) 92.0% name _________________ 15. Which of the following statements is false? a) If you combine a sample of sodium chloride weighing exactly 2 g with a sample of potassium bromide weighing exactly 2 g, the resulting mixture will weigh exactly 4 g. b) If you combine exactly 10 mL of 1.0 M aqueous sodium chloride with exactly 10 mL of 1.0 M potassium bromide, the resulting mixture will have a volume of exactly 20 mL c) 14C and 14N have exactly the same mass number. d) All isotopes of a given element have exactly the same number of protons. e) All neutral atoms have exactly the same number of protons as the number of electrons. 16. 4.14 g of an unknown metal reacts with excess oxygen gas, O2, to make 4.45 g of a black powder. The empirical formula of the product in M2O. What is M? a) Li b) Na c) K d) Cu e) Ag f) Hg 17. What volume of 0.362 M HCl must be diluted to a final volume of 250.00 mL to obtain a solution that is 0.0995 M HCl? a) 33.29 mL b) 45.73 mL c) 59.10 mL d) 68.7 mL e) 80.90 mL 18. Professor Yee has performed a number of demonstrations in class. Which of the following set of reactants is not the starting material for a redox reaction? a) “Flames of Hell”, Al(s) + Br2(l) b) “Lightbulb indicator”, Ba(OH)2(aq) + H2SO4(aq) c) “Dry ice lamp”, Mg(s) + CO2(s) d) “Thermite”, Al2O3(s) + Fe(s) e) “Copper wire in silver solution”, Cu(s) + AgNO3(aq) f) All are redox reactions name _________________ THIS IS TEST VERSION A Short answer questions 19. Some elements exist in nature as only a single isotope. The following is a list of five such elements, plus element that does not exist as a single isotope. Figure out which one does not exist as a single isotope and explain your reasoning. No credit for guessing. Be, F, Na, Mg, Al, P The atomic mass of single isotope elements must be very close to a whole number because every atom is identical and has the same number of protons and neutrons and because protons and neutrons weigh almost exactly 1 amu. Be (9.01), F (19.00), Na (22.99), Al (26.98) and P (30.97). Because Mg consists of multiple isotopes, its average atomic mass can be away from a whole number. (24.30) 20. An unknown diprotic acid consisting of only C, H and O is subjected to combustion analysis and this yields 57.83% C and 3.61% H. A 1.000 g sample is titrated with 0.300 M sodium hydroxide and it requires 39.20 mL to reach the equivalence point. What is the molecular formula of the unknown? Show all of your work for full credit. Assume 100 g. Then 57.83 g of C, 3.61 g of H and 38.56 g of O Converting to moles: C4.82 mol, H 3.58 mol and O 2.41 mol  C4.82H 3.58O2.41 Dividing by 2.41  C2H1.5O  C4H3O2 empirical formula (2 pt) H2A +2 OH-  2H2O + A2- Mol of OH- = 0.03920 L x 0.300 L = 0.01176 mol OH Mol of H2A = 0.01176 mol OH x 2 mol OH/1mol H2A = 000588 mol H2A Molar mass of H2A = 1.000 g/0.00588 mol = 170 g/mol Empirical formula mass = 83 g/mol ~ 1/2 molar mass Molecular formula = C8H6O4