Name Student ID Number Lab TA Name and Time CHEMISTRY 2A Exam I Fall 2012 - Enderle Instructions: CLOSED BOOK EXAM! No books, notes, or additional scrap paper are permitted. All information required is contained on the exam. Place all work in the space provided. If you require additional space, use the back of the exam. (1) Read each question carefully. (2) There is no partial credit for the problems in Part I and Part II. You will lose 10 points if you do not circle your multiple choice answers on the front page or if you do not write your TA s name in the space above. (3) The last page contains a periodic table and some useful information. You may remove this for easy access. (4) Graded exams will be returned in the laboratory sections next week. (5) If you finish early, RECHECK YOUR ANSWERS! U.C. Davis is an Honor Institution Possible Points Points 1 11. 33 points 12 14. 13 points Multiple Choice (circle one) 1. A B C D E 2. A B C D E 3. A B C D E 4. A B C D E 5. A B C D E 6. A B C D E 7. A B C D E 8. A B C D E 9. A B C D E 10. A B C D E 11. A B C D E 15 17. 27 points 18 20. 14 points 21 23. 20 points Total Score (107)
Exam I Page 2 of 7 Part I: Multiple Choice Circle the correct answer here and on the cover No partial credit (3 points each) 1. A cup of water was left out undisturbed. At that time the water had a density of 1.0 g/ml. After one week, the cup was half full by volume. What is density of water in the cup now? A. 0.25 g/ml B. 0.50 g/ml C. 1.0 g/ml D. 1.5 g/ml E. 2.0 g/ml 2. Consider the general chemical equation: 3 A + 2 B 5 C 15.0 mol of A react with 9.0 mol of B. Predict the limiting reactant. A. A B. B C. C D. A and B E. none of them 3. Fluorine is a member of the family called. A. metals B. metalloids C. noble gases D. halogens E. actinides 4. If 2.54 g of sodium benzoate is dissolved in 75.00 g H 2 O, what is the mass % of sodium benzoate? A. 3.39 % B. 29.5 % C. 0.327 % D. 3.28 % E. 0.03386 % 5. Calculate the percent mass of nitrogen in ammonium nitrate. A. 17.5 % B. 21.9 % C. 22.9 % D. 35.0 % E. 36.1 % 6. Which of the following chemical equations represents a single replacement reaction? A. H 2 SO 4 + 2NaOH 2 H 2 O + Na 2 SO 4 B. 2 AgNO 3 + CuCl 2 2 AgCl + Cu(NO 3 ) 2 C. NaCl + NH 4 Br NaBr + NH 4 Cl D. Mg + 2 HCl MgCl 2 + H 2 E. CaCO 3 CaO + CO 2 7. A 2.0 gal flask weighs 4.0 lbs. when empty. When it is filled with liquid, the flask weighs 4536.0 g. What is the density of the liquid in g/ml? (1 gal = 3.785 L, 1 lb. = 453.6 g) A. 0.36 g/ml B. 0.72 g/ml 4536.0g 4(453.6g) = 2721.6g C. 0.60 g/ml d = 2721.6g/(2.0(3.785L)1000) = 0.36g/mL D. 0.14 g/ml E. 0.071 g/ml 8. Which statement below is true? A. Chlorine is in the halogen family. B. Oxygen is in the third period. C. Potassium is in the alkali earth family. D. Tin is a transition metal. E. Mercury is one of the lanthanides.
Exam I Page 3 of 7 9. When a chemical reaction is carried out in a sealed container, the substances may change in color temperature, or state, but no change in mass is detected. This is evidence of the: A. law of conservation of mass B. law of constant composition C. law of definite proportions D. existence of electrons E. existence of protons 10. Which of the following statements is FALSE? A. Faraday determined that cathode rays were the fundamental negatively charged particles and called them electrons. B. Thomson suggested the "plum pudding" model of the atom. C. Millikan determined the charge on an electron. D. Thomson determined the charge-to-mass ratio for electrons. 11. With mass spectral data the ratio of the mass of 14 N/ 12 C was found to be 1.167. What is the mass of the 14N atom? A. 14.017 u B. 10.292 u C. 14.004 u D. 17.000 u E. 14.007 u Part II: Short Answer Fill in the blank 12. (4 points) Balance. 2 KMnO4 + 10 KI + 8 H2SO4 6 K2SO4 + 2 MnSO4 + 5 I2 + 8 H2O 13. (6 points) Given the organic molecule, determine the name, molecular formula, and empirical formula. Name: hexane Molecular formula: C 6 H 14 Empirical formula: C 3 H 7 14. (3 points) Give the number of significant figures in each of the following measurements. A. 3.408 x 10 4 4 B. 463.090 6 C. 0.0005890 4
Exam I Page 4 of 7 15. (6 points) Fill in the table by determining if the listed compounds are strong or weak electrolytes. In the first example, the strength of the acid is listed. Compound H 2 SO 4 (aq), strong acid CO 2 (g) NaNO 3 (aq) Strong or Weak Electrolyte? Strong Weak Strong 16. (17 points) Fill in the blanks of the table giving the chemical name or chemical formula. In addition, give the oxidation state of the indicated element. Chemical Formula Chemical Name Ox. State Mg 3 N 2 magnesium nitride N: -3 H 2 CO 3 carbonic acid H: +1 HF hydrofluoric acid F: -1 N 3 S 6 trinitrogen hexasulfide Skip this box Cu(OH) 2 cupric or copper(ii) hydroxide Cu: +2 Pb(Cr 2 O 7 ) 2 plumbic dichromate Cr: +6 17. (4 points) Write the balanced equation for the following reactions. A. The reaction of mixing sulfuric acid and sodium hydroxide in solution. H 2 SO 4 + 2NaOH 2 H 2 O + Na 2 SO 4 B. The reaction from mixing silver(i) nitrate and cupric chloride in solution. 2 AgNO 3 + CuCl 2 2 AgCl + Cu(NO 3 ) 2
Exam I Page 5 of 7 18. (3 points) Find the total number of protons, neutrons, and electrons in the carbonate ion. You may round the mass numbers from the periodic table to the nearest whole numbers in order to find the number of neutrons. Protons = 30 Electrons = 32 Neutrons = 30 Part III: Long Answer Please show all work Partial credit Use the correct number of significant figures 19. (4 points) Consider a hypothetical sample of matter that contains only two types of atoms: boron-10 (molar mass = 10.013 g/mol) and boron-11 (molar mass = 11.009 g/mol). If the hypothetical sample contains three times as many boron-11 atoms as boron-10 atoms, then what is the molar mass of the sample? Molar Mass = 10.013 (0.25) + 11.009 (0.75) = 10.760 M.M. (g/mol) = 10.760 20. (7 points) The percent yield in oxygen for the following reaction is 65.0%. How many grams of KClO3 are needed to produce 32.0 g of O2? 2 KClO3(s) 2 KCl(s) + 3 O2(g) % Yield = (Actual / Theoretical) x 100 65.0 = 32.0 g O 2 /Theoretical Theoretical = 49.23 g O 2? g KClO 3 = (49.23 g O 2 )(1 mol O 2 /32g O 2 )(2 mol KClO 3 /3mol O 2 ) (122.5 g KClO 3 / 1 mol KClO 3 ) = 125.6 g KClO 3 g KClO 3 = 126 g
Exam I Page 6 of 7 21.(6 points) A student prepared a stock solution by dissolving 10.0 g of KOH in enough water to make 150.0 ml of solution. What volume of the stock solution is needed to make 0.065 L of 0.277 M solution? 10. g KOH /56.1 g/mol = 0.178 moles of KOH 0.178 mol of KOH/0.15 L of solution = 1.2 M M 1 V 1 = M 2 V 2 (1.2)(V) = (65)(0.277) V = 15 ml V = 15 ml 22. (7 points) The organic solvent thiophene is a carbon-hydrogen-sulfur containing compound that yields CO 2, H 2 O, and SO 2 when burned in excess oxygen. When a 1.3020g sample of thiophene is combusted, 2.7224g of CO 2, 0.5575g of H 2 O, and 0.9915g of SO 2 are produced. What is the empirical formula of thiophene? (2.7224g CO 2 ) x(1 mole CO 2 / 44g CO 2 ) x(1 mole C /1 mole CO 2 ) = 0.0619 mol C (0.5575 g H 2 O) x (1 mole H 2 O/18.02g) x (2 mol H/1 mole H 2 O) = 0.0619 mol H (0.9915g SO 2 ) x (1mole SO 2 / 64g) x (1 mol S/1 mole SO 2 ) = 0.0155 mol S C 0.0619 H 0.0619 S 0.0155 then divide by the smallest. C 4 H 4 S 23. (7 points) If 8.52 g each of zinc, potassium dichromate, and sulfuric acid are reacted by the reaction: 4 Zn + K2Cr2O7 + 7 H2SO4 4 ZnSO4 + 2 CrSO4 +K2SO4 + 7 H2O How many grams of potassium dichromate will be left unreacted if sulfuric acid is limiting? (8.52 g)(mol/ 98.0791 g)(1 mol/7 mol)(294.185 g/mol K2Cr2O7) = 3.65 g K2Cr2O7 8.52 g 3.65 g = 4.87 g K2Cr2O7 unreacted g K2Cr2O7 unreacted = 4.87 g
Exam I Page 7 of 7 Avogadro s number = 6.022 x 10 23 / mol M 1 V 1 = M 2 V 2 d = m/v