Chem 127, Final Exam December 13, 2002

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1 I. (55 points) This part of the final corresponds to Exam I. It covers the material in Chapters 1, 2 and 3. A. (20 points) The following questions are NOT related to each other. 1. Express 1 part per million in ng (nanograms)/gram. 2. The density of concentrated sulfuric acid is 1.85 g/ml. What volume of the acid would have a mass of 74.0 g? 3. One cubic millimeter (mm 3 ) of oil is spread on the surface of the water so that the oil film has an area of one square meter (m 2 ). What is the thickness of the oil film in nanometer (nm) units? 4. What is the chemical formula for sodium hypochlorite? 5. What is the name of the compound HNO 2 (aq)? 1

2 B. (15 points) The following questions are NOT related to each other. 1. Liquid helium boils at 4 K. What is its boiling point on the Fahrenheit scale? 2. Consider sodium phosphate. a. Write its formula. b. How many moles of sodium ions are present in 25.0 ml of M of sodium phosphate? 3. What is the mass percent of hydrogen in ammonia? 2

3 C. (10 points) Magnesium atoms react with bromine atoms in a ratio of 1 atom to 2 atoms respectively. 1. How many grams of Br 2 will combine with 33.3 g of magnesium? 2. If 1.00 g of magnesium reacts with 5.00 g of Br 2, how many grams of product are produced? D. (10 points) Consider acetylene, C 2 H 2 (g) 1. Write a balanced net ionic equation using smallest whole number coefficients for the combustion of acetylene to water and carbon dioxide. Do not forget to write the states of the species in the reaction. 2. What are the masses of CO 2 and H 2 O produced when 104 g of C 2 H 2 is burned? CO 2 = H 2 O= 3

4 II. (70 points) This part of the final corresponds to Exam II. It covers the material in Chapters 4 and 5. A. (18 points) Identify the the type of aqueous reaction on the blanks to the left using the symbols PPT for precipitation SA/SB for strong acid/strong base SA/WB for strong acid/weak base WA/SB for weak acid/strong base NR for no reaction Write all the products of the reaction or NR on the blanks to the right. Do not include spectator ions. CH 3 CH 2 NH 2 + HCl Ca(OH) 2 +Na 3 PO 4 Ag 2 SO 4 + BaCl 2 Ba(NO 3 ) 2 +NH 4 Cl B. (10 points) Balance the following redox equation in acidic medium and answer the following questions. (You may balance this equation at the bottom of the page.) HBrO 3 (aq) + Bi (s) HBrO 2 (aq) + Bi 2 O 3 (s) 1. What species is the oxidizing agent? 2. What element is reduced? 3. What is the oxidation number of Br before the reaction? 4. How many electrons does each Bi gain or lose? 5. What is the coefficient of water in the final balanced equation? 4

5 C. (14 points) For the following questions consider a M solution of strontium hydroxide. 1. How many moles of OH are present in 67.3 ml of this solution? 2. What volume of this solution is required to react completely with 35.0 ml of M Na 2 CO 3? [Note: You will be eligible for partial credit if you write a balanced net ionic equation.] 3. What volume of this solution is required to react completely with 25 ml of M HF? [Note: You will be eligible for partial credit if you write a balanced net ionic equation.] D. (5 points) Consider the following reaction between sulfur dioxide gas and chlorine. SO 2 (g) + 2Cl 2 (g) SOCl 2 (l) +Cl 2 O (g) What volume of Cl 2 O gas can be obtained under conditions of constant temperature and pressure if 42 L of SO 2 are made to react with 42 L of chlorine? 5

6 E. (15 points) The following 3 questions are NOT related. 1. Argon effuses twice as fast as what diatomic molecule? 2. A sample of neon gas has a volume of 10.0 liters at 27 C. At constant pressure, and 177 C, what is the volume of that sample? 3. At K and 1.00 atm, what mass of helium gas has the same volume as one mole of oxygen molecules? F. (8 points) A 10.0 L flask at 280 K contains chlorine, helium and nitrogen gases. The total pressure in the flask is 1.1 atm. a) How many moles of gas are in the flask? b) What is the partial pressure of chlorine if there are 12.5 g of chlorine in the flask? 6

7 III. (70 points) This part of the final corresponds to Exam III. It covers the material in Chapters 6, 7 and 8. A. (10 points) The following 2 problems are NOT related. 1. Electric power lines carrying alternating current emit photons with a frequency of 60 s 1 (= 60 Hz). What is the wavelength of the photons in kilometers? 2. In medical procedures, a radioactive isotope of technicium (Tc) emits gamma rays (of very short wavelength) with an energy of 2.24 x J (= 0.14 MeV). What is the wavelength of the gamma rays in meters? B. (18 points) Given beow are possible electron configurations for boron (B). (The same letter may be used more than once or not at all.) (a) 1s 2 2s 2 2p 1 (b) 1s 2 2s 2 2p 2 (c) 1s 1 2s 1 2p 2 3s 1 (d) 1s 2 2s 2 2d 1 1. Which electron configuration is the ground state for boron? 2. Which electron configuration is the ground state for a B ion? 3. Which electron configuration could have all the electrons with the same spin? 4. Which electron configuration is possible for boron in the excited state? 5. Which electron configuration is impossible? 6. Which electron configuration has the largest ionization potential? C. (5 points) Write the Lewis structure for SCN (C = central atom) in the box provided. 7

8 D. (9 points) S 2 Cl 2 (disulfur dichloride) is an orange liquid with a revolting smell. It has the following Lewis structure. Cl S S Cl 1. Does this structure have any other resonance forms? 2. What is the molecular geometry about one of the S atoms? 3. What are the formal charges on the S atoms? E. (9 points) SOF 4 has the following Lewis structure. 1. Describe its geometry in words. 2. Is the compound polar? 3. What is the hybridization of the sulfur atom? F. (19 points) Consider the following standard enthalpies of formation (in kj/mol) and the reaction for dissolving NaOH in water. NaOH (s) = Na + (aq) = OH (aq) = What is H for the reaction? NaOH (s) Na + (aq) + OH (aq) 2. Is the reaction exothermic? 8

9 3. In a coffee cup calorimeter, mol of NaOH are dissolved in g of water at 25 C. a. What is q for the solution? b. What is the final temperature of the solution? 4. What is H for the following reaction? 2 NaOH (s) 2Na(s)+O 2 (g) + H 2 (g) 9

10 IV. (55 points) This part of the final covers the material in Chapter 9. A. (10 points) Write your answers on the blanks provided. Consider the following compounds at 25 C. Hg, CH 3 CH 2 CH 2 OH, Na 2 S, CH 3 COCH 3, C (graphite) Answer the following questions. 1. Which compound is a metal? 2. Which compound has the lowest boiling point? 3. Which compound has ionic bonds? 4. Which compound is network covalent? 5. Which compound has hydrogen bonding? B. (10 points) Answer the questions below, using LT (for is less than ), GT (for is greater than ), EQ (for is equal to ), or MI (for more information required ) in the blanks provided. 1. At 50 C, benzene has a vapor pressure of 269 mm Hg. A flask that contains both benzene liquid and vapor at 50 C has a pressure (1) 269 mm Hg 2. Ether has a vapor pressure of 537 mm Hg at 25 C. A flask that contains only ether vapor at 37 C has a pressure (1) 537 mm Hg. 3. The boiling point of H 2 O 2 (1) the boiling point of C 3 H The energy required to vaporize liquid bromine (1) the energy required to decompose Br 2 into Br atoms. 5. The dispersion forces present in naphthalene, C 10 H 8, (1) the dispersion forces present in butane, C 4 H

11 C. (15 points) Consider the phase diagram for compound A given below. Answer the following questions by referring to the diagram. 1. What is the physical state of A at 500 mm Hg and 50 C? 2. Consider A at 25 C and 700 mm Hg. If the pressure is kept constant, what phase change for A takes place first as the temperature is increased? 3. What is the normal boiling point of A? 4. Is the density of A (s) larger than the density of A (l)? 5. Consider A at 25 C and 300 mm Hg. If the temperature is kept constant and the pressure is reduced to 2 mm Hg, what happens to A? D. (5 points) Aluminum has atomic radius of nm and crystallizes with a facecentered cubic unit cell. What is the volume of a unit cell of aluminum? 11

12 E. (15 points) Consider the information given below about methyl alcohol (CH 3 OH). molar mass = g/mol density = g/ml vapor pressure at 35 C = 203 mm Hg Heat of vaporization ( H vap ) = 35.4 kj/mol 1. A 10.0 ml sample of methyl alcohol is poured into a 4.0 L flask. The flask is sealed and the temperature kept at 35 C. Both liquid and gas are in the flask. a. How many moles of CH 3 OH are present in the flask as gas? b. How many ml are present as liquid? 2. What is the normal boiling point of methyl alcohol? 12

13 BONUS (15 points) All or nothing. The bonus should be done only after you have completed the main part of this exam and checked your work for errors. The time allotted for this exam does not include time for the bonus. (SHOW ALL WORK! Lucky guesses will not be considered.) The total pressure of a mixture of oxygen and hydrogen is 1.00 atm. The mixture is ignited and the water formed is removed. The remaining gas is pure hydrogen with a pressure of 0.40 atm when measured under the same conditions of temperature and volume as the original mixture. What was the original mole percent composition of the mixture? 13

Chem 127, Final Exam December 14, 2001

Chem 127, Final Exam December 14, 2001 I. (55 points) This part of the final corresponds to Exam I. It covers the material in Chapters 1, 2 and 3. A. (8 points) Fill in the empty boxes with the appropriate symbol, number, word or charge. Nuclear