Chem 127, Final Exam December 14, 2001

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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. (8 points) Fill in the empty boxes with the appropriate symbol, number, word or charge. Nuclear symbol 40 Ca Ag + Protons 47 Neutrons (name of subatomic particle) Mass Number 107 Atomic Number Net Charge 0 1

2 B. (8 points) Determine whether the statements given below are true or false. Write Y if the statement is true, and N if the statement is false in the blanks provided. Do not usetorf. 1. All the isotopes of an element have the same number of protons but varying numbers of neutrons. 2. The horizontal rows in a periodic table are referred to as periods. 3. Crystals of iodine can be classified as a heterogeneous mixture. 4. The mass (in grams) of one mole of nitrogen molecules is C. (16 points) Write the formulas or names of the following compounds. 1. Sulfur dioxide 2. Tin(II) nitrate 3. Perchloric acid 4. ammonia 5. CH 4 6. AlBr 3 7. Fe 2 (SO 3 ) 3 8. IBr 3 2

3 D. (8 points) Consider acetic acid C 2 H 4 O 2 1. What is its molar mass in grams? 2. What is its simplest formula? 3. When acetic acid is burned in air, carbon dioxide and water are produced. Balance the equation for this reaction by writing the appropriate coefficients on the blanks provided. C 2 H 4 O 2 (l) + O 2 (g) CO 2 (g) + H 2 O(l) E. (6 points) Consider ethyl alcohol, C 2 H 6 O, (M = 46.1 g/mol). 1. How many grams of hydrogen can be obtained from 138 g of ethyl alcohol? 4. What is the mass percent of carbon in ethyl alcohol? 3

4 F. (9 points) Consider the following balanced equation: 2Sb(s) + 3F 2 (g) 2 SbF 3 (s) To produce SbF 3 (M = g/mol), 5.00 g of Sb (M = g/mol) and 5.00 g of F 2 (M = g/mol) are mixed together. 1. How many moles of Sb are present before reaction? 2. How many moles of F 2 are present before reaction? 3. What is the limiting reactant? 4. Assuming 100% yield how many grams of SbF 3 are produced after reaction is complete? 4

5 II. (70 points) This part of the final corresponds to Exam II. It covers the material in Chapters 4 and 5. A. (8 points) Write your answers to the following questions on the space provided. You may do your calculations on the scratch paper provided. These will not be graded. Consider ml of M FeCl 3. The next 4 questions refer to this solution. 1. How many moles of chloride ions are present in this solution? 2. When NaOH reacts with FeCl 3, the following reaction occurs: Fe 3+ (aq) + 3 OH (aq) Fe(OH) 3 (s) How many moles of NaOH are required to completely react with this solution of FeCl 3? 3. How many ml of this solution are required to prepare 1.00 L of a M solution of FeCl 3? 4. When an oxidizing agent is added to the FeCl 3 solution, chlorate ions are formed. Cl (aq) ClO 3 (aq) +? e How many electrons are lost in this oxidation? B. (12 points) Write the formula(s) of the product(s) obtained by mixing aqueous 0.1M solutions of the following compounds. Write NR if there is no reaction Do not include spectator ions. 1. HCl and KOH 2. H 2 SO 4 and Ca(NO 3 ) 2 3. NaOH and ZnCO 3 4. HNO 2 and Sr(OH) 2 5. NH 3 and HClO 4 5

6 C. (10 points) Balance the following equation in acid medium. Do your work on the scratch paper provided. Answer the following questions about the balanced equation in the blanks provided. Al 3+ (aq) + SO 2 3 (aq) Al (s) + SO 2 4 (aq) 1. What is the oxidation number for sulfur in SO 2 3? 2. What is the reducing agent? 3. How many electrons are gained in the reduction half-reaction? 4. How many moles of H + ions are present in the balanced redox equation? 5. What is the coefficient of the sulfate ion in the balanced redox equation? D. (4 points) Aluminum nitrate (Al(NO 3 ) 3 ) reacts with NaOH to form a precipitate according to the following balanced equation. Al 3+ (aq) + 3 OH (aq) Al(OH) 3 (s) Assuming 100% yield, how many ml of M NaOH are required to produce g of Al(OH) 3 (M = g/mol)? 6

7 E. (6 points) A sample of an alloy made up of zinc and a nonreactive metal is analyzed by treatment with nitrate ion in basic solution. The following is a balanced equation for the redox reaction that occurs. 4 Zn (s) + 7 OH (aq) + NO 3 (aq) + 6 H 2 O 4 Zn(OH) 2 4 (aq) + NH 3 (aq) If ml of M sodium nitrate is used to furnish the nitrate ions, what is the minimum volume of M barium hydroxide needed to furnish enough hydroxide ions? Assume 100% yield. F. (10 points) Consider 3 sealed tanks all at the same temperature, pressure and volume. Tank A contains SO 2 gas Tank B contains O 2 gas Tank C contains CH 4 gas Fill in the blanks on the left, using LT (for is less than), GT (for is greater than), EQ (for is equal to),or MI (for more information required). 1. The mass of SO 2 in Tank A the mass of O 2 in Tank B. 2. The kinetic energy of CH 4 in Tank C the kinetic energy of SO 2 in Tank A. 3. It takes 20 seconds for all of the O 2 gas in Tank B to effuse out of a pinhole in the tank. The time it takes for all of the SO 2 to effuse out of Tank A from an identical pinhole 40 seconds. 4. The density of O 2 in Tank B the density of CH 4 in Tank C. 5. The temperature in Tank A is increased from 150 K to 300K. The temperature in Tank B is kept at 150 K. The pressure in Tank A is half the pressure in Tank B. 7

8 G. (15 points) Write your answers to the problems in the blanks provided. Do your calculations on scratch paper. Only the answers on the blanks will be considered. 1. A 0.50 L sample of gas in a closed container at 0.50 atm is compressed to 0.10 L at constant temperature. What is the pressure of the gas after compression? 2. Hydrogen gas is collected over water at 758 mm Hg. The vapor pressure of water is 22 mm Hg. What is the pressure of the dry gas in mm Hg? 3. Neon gas effuses out of a pinhole at the rate of 200 ml/s. At the same temperature, what is the rate at which another gas with a molar mass of 80 g/mol effuses? 4. A flask contains 10.0 g of Ar and 3.00 g of He. The total pressure is 1.00 atm. What is the partial pressure of Ar? 5. A 4.00 L flask has 38.0 g of fluorine gas at 300 K. What is the pressure of the gas in the flask? H. (5 points) Nitric acid can be prepared by bubbling dinitrogen pentoxide (N 2 O 5 ) into water according to the following reaction. N 2 O 5 (g)+h 2 O 2H + (aq) + 2 NO 3 (aq) 1.50 L of N 2 O 5 at 25 C and 1.00 atm is bubbled into water. The total volume of the aqueous solution of nitric acid obtained is 437 ml. Assuming 100% yield, what is the molarity of the nitric acid solution obtained? 8

9 III. (70 points) This part of the final corresponds to Exam III. It covers the material in Chapters 6, 7, and 8. A. (20 points) Write your answers in the blanks provided. 1. How many electrons can an atom have with quantum numbers n=3,l =2, and m s = 1/2? 2. How many d electrons are in the ground state of Zn? 3. How many d electrons are in the ground state of Zn 2+? 4. How many unpaired electrons are there in an atom of phosphorus? 5. How many unpaired electrons are there in an atom of chlorine? 6. What is the symbol of the element with the smallest radius in Group 16? 7. What is the symbol of the element with the highest first ionization energy in Period 4? 8. What is the symbol of the element with a +4 ion that has the abbreviated electron configuration: [Kr] 4d 6? 9. What is the symbol of the most electronegative element in Group 17? 10. Write the orbital diagram for oxygen in the ground state by putting up and down arrows in the empty orbitals provided below. Label the orbitals that you use. ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 9

10 B. (6 points) What wavelength is associated with a transition from n = 10 to n = 5? In this transition is energy absorbed or given off? C. (19 points) Write your answers on the blanks provided. 1. Predict the molecular geometry of NH Predict the molecular geometry of IF What is the hybridization of C in HCN? 4. How many pi bonds does N 2 have? 5. How many sigma bonds does CO 2 have? Consider 2 possible Lewis structures for SeO 3 (labeled A and B) given below :O.. Se O:.. :O=Se=O: :O: :O: (A) (B) 8. How many different resonance structures can be written for for Structure A? (Count the one given as the first one.) 9. Which structure gives the minimum formal charge for all atoms? 10

11 D. (6 points) Consider the following molecules whose Lewis structure is given. In the box provided, write P if the molecule is polar, and NP if the molecule is nonpolar. E. (6 points) Given the following data: H fus for benzene (C 6 H 6 ) = 9.84 kj/mol H vap for water = 40.7 kj/mol 1. Which process absorbs more heat, freezing 5.00 mol of benzene or vaporizing 1.00 mol of water? 2. How many joules of energy does your chosen process require? 11

12 F. (7 points) Five cent coins (nickels) weigh 5.0 g. After 30 cents worth of nickels at 100 C are placed in a coffee cup calorimeter containing 50.0 g of water at 22 C, the temperature of the water is 30.0 C. Specific heat of water = 4.18 J/g C 1. How many joules of heat are absorbed by the water? 2. What is the specific heat of nickel? G. (6 points) Given the following thermodynamic equations: 2H 2 (g) + O 2 (g) 2H 2 O(l) H = kj N 2 O 5 (g) + H 2 O(l) 2 HNO 3 (l) H = 73.7 kj N 2 (g) + 3 O 2 (g)+h 2 (g) 2 HNO 3 (l) H = kj Use Hess s Law to calculate H for the reaction N 2 (g) + 5/2 O 2 (g) N 2 O 5 (g) Write the H values that you sum to find your answer on the line below. + + = 12

13 IV. (55 points) This part of the final corresponds to Chapter 9. A. (14 points) Consider the phase diagram for CCl 4 given below. Answer the questions about the diagram by writing your answers on the blanks provided. 1. What point (not including the triple point) represents an equilibrium between the solid and the vapor phase? 2. What is CCl 4 at point G called? 3. Does the boiling point increase as pressure above the liquid is decreased? (Yes or No) 4. What point represents CCl 4 only in the gas phase? 5. Does the melting point increase as pressure is applied to the solid? (Yes or No) 6. Is sublimation of CCl 4 impossible at any pressure? (Yes or No) 7. For a specific temperature above point E, the density of the liquid phase is larger than the density of the solid phase. (Yes or No) 13

14 . B. (12 points) Answer the following questions. 1. The important intermolecular force in I 2 crystal is: Circle one metallic network covalent ionic dispersion dipole hydrogen bonding 2. Write all the intermolecular forces present in both CH 3 Cl and CH 3 I. 3. CH 3 Cl has a lower boiling point than CH 3 I. What intermolecular force accounts for this phenomenon? Consider the following vapor pressure diagram. 4. Which liquid has a higher boiling point? 5. Which liquid would evaporate more quickly? 14

15 C. (18 points) Consider chloroform (CHCl 3 ). It has the following properties: melting point = 63 C vapor pressure at 25 C = 213 mm Hg H vap = 29.2 kj/mol 1. A flask with a volume of 2.00 L is sealed at 25 C after mol of CHCl are added. What is the pressure in the flask? 2. What phase(s) of chloroform is/are present in the flask described in (1)? 3. What is the maximum volume that the flask described in (1) can have so that both phases of CHCl 3 are present? 4. What is the vapor pressure of chloroform at 45 C? 15

16 D. (5 points) An element X crystallizes with a simple cubic cell. The volume of a cell is nm 3. What is the radius of an atom of X? E. (9 points) Consider the following substances (Lewis structures may be necessary in some cases.): CO 2 HF KO 2 K SO 2 diamond Match the substance(s) with the following properties. Note that you can write more than one answer on the blank and that you may use the substance as an answer more than once. 1. is an ionic compound. 2. has hydrogen bonding. 3. has dipole forces 4. has dispersion forces. 5. conducts electricity well in the solid. 6. is network covalent. 16

17 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.) When magnesium metal burns in air, it reacts with oxygen to form magnesium oxide and with nitrogen to form magnesium nitride. Magnesium nitride reacts with water to form magnesium oxide and ammonia gas. In a particular experiment, a piece of magnesium was burned in air to give g of a mixture of magnesium oxide and magnesium nitride. Water was added and the mixture was heated until g of dry MgO remained. What is the mass percent of magnesium nitride in the mixture of magnesium oxide and magnesium nitride? 17

Chem 127, Final Exam December 10, 2003

Chem 127, Final Exam December 10, 2003 I. (55 points) This part of the final corresponds to Exam I. It covers the material in Chapters 1, 2 and 3. A. (10 points) Answer the following questions by writing your answers on the blanks provided.