CHEMISTRY 222 Rogue Community College HOMEWORK SHEETS WINTER 2014 to be used with McQuarrie, Rock and Gallogly, General Chemistry (4 th edition) Structures of Molecules & Polyatomic Ions (CH. 8/9)........ 1 Molecular Orbitals (CH. 9)....... 3 Gas Laws (CH. 13).. 5 Gas Calculations (CH. 13)... 7 Intermolecular Forces (CH. 15)..... 9 Condensed Phases (CH. 15) 11 Solutions I (CH. 16).... 13 Solutions II (CH. 16) 15 Kinetics I (CH. 17)... 17 Kinetics II (CH. 18)...... 19 Equilibrium I (CH. 19)..... 21 Equilibrium II (CH. 19).... 23 Acid/Base I (CH. 20).... 25 Acid/Base II (CH. 20)... 27
Chemistry 222, Rogue Community College Structures of Molecules & Polyatomic Ions Homework (Ch. 8/9) Name Molecular Formula Number of v.e. Lewis Structure Shape Hybridization (central atom) Polar or Nonpolar? H 2 O NH 3 CH 4 SCl 6 PCl 5 CO 2 HCN SO 2 SO 3 1
(note that the last column is a different question on the back than on the front) Polyatomic Ion Number of v.e. Lewis Structure Shape Hybridization (central atom) Numbers of and bonds NH 4 + H 3 O + CO 3 2 NO 3 IF 4 + N 3 ClO 3 NH 2 ICl 4 BrO 2 2
Chemistry 222, Rogue Community College Molecular Orbitals Homework (Ch. 9) Name 1. Two atomic orbitals can interfere with each other to make two molecular orbitals. (a) What is the name of the molecular orbital formed by constructive interference (i.e. with most of its electron density in between the two nuclei)? (b) What is the name of the molecular orbital formed by destructive interference (i.e. with most of its electron density on the far sides of the two nuclei)? 2. Sketch the molecular orbital energy diagram showing the addition and subtraction of two 1s atomic orbitals to form 1s and *1s molecular orbitals. 3. Use the diagram you drew for question #2 to determine the bond order for each of the following diatomic molecules (or ions). Number of Electrons Bond Order H2 H2 + H2 He2 He2 + 3
4. Sketch two molecular orbital energy diagrams showing the interference of two 2s and six 2p atomic orbitals to form 2s, *2s, 2p, *2p, 2p, *2p molecular orbitals. Be sure to label which diagram is used for lithium/beryllium/boron/carbon/nitrogen and which diagram is used for oxygen/fluorine/neon. 5. Use the diagrams you drew for question #4 to determine the bond order for each of the following diatomic ions. Use the same diagram for each ion that you would for the neutral molecule. Number of Electrons Bond Order C2 + O2 + C2 O2 NO + NO 6. Which common diatomic element is paramagnetic? In which molecular orbitals are the unpaired electrons found? Note: this is a major success for molecular orbital theory because neither the Lewis structure nor the valence bond model, can explain this observation. 4
Chemistry 222 Rogue Community College Gas Law Homework (Ch. 13) Name Ideal Gas Law: PV = nrt, where R = 0.08206 Latm/molK Boyle's Law: P1V1 = P2V2 (n, T constant); Charles' Law: V1/T1 = V2/T2 (n, P constant) 1. What is the volume of 3.25 moles of ideal gas at 25.0 C and 0.759 atm pressure? 2. What pressure is exerted by 0.25 moles of ideal gas at 50.0 C and a volume of 1.75 L? 3. How many moles of ideal gas will occupy a volume of 20.0 L at 100. C and 0.275 atm? 5
4. At what temperature (in C) will 1.25 moles of ideal gas occupy a volume of 10.0 L with a pressure of 0.500 atm? 5. A fixed quantity of gas at 25.00 C occupies 3.75 L. If the gas is heated at constant pressure to 50.00 C, what will its new volume be? 6. A fixed quantity of gas at 2.75 atm occupies 3.75 L. If the gas is compressed at constant temperature to 1.75 L, what will its new pressure be? 7. For the following reaction, (a) calculate the mass of aluminum required in order to produce 25.0 ml of H2 gas at 23.5 C and 0.805 atm, and (b) calculate the volume of 0.150 M HCl required in order to react completely with the mass of aluminum you calculated in part (a). 2 Al (s) + 6 HCl (aq) 3 H2 (g) + 2 AlCl3 (aq) 6
Chemistry 222 Rogue Community College Gas Calculations Homework (Ch. 13) Name 1. What is the density of methane gas at STP? 2. The density of a gas is measured at STP and found to be 1.428 g/l. What is the molecular weight of the gas? What could be the identity of the gas? 3. If 3.095 g of a pure gaseous substance is found to occupy 3.846 L at 22 C and 0.975 atm, what is the molecular weight of the gas? What is the probable identity of the gas? 4. If a mixture of 10.7% (by volume) CO and 89.3% (by volume) CO2 exerts a total pressure of 1.75 atm, what are the partial pressures of CO and CO2 in the mixture? 5. If a mixture of 5.25 g CO and 8.43 g CO2 exerts a total pressure of 1.75 atm, what are the partial pressures of CO and CO2 in the mixture? 7
6. A 98.5 ml sample of H2 gas is collected over water at STP. If the vapor pressure of water is 0.0325 atm at this temperature, how many moles of H2 were collected? 7. Which of the following gases has the greatest average molecular kinetic energy at STP? (A) H2 (B) He (C) N2 (D) all are the same 8. Which of the following gases has the greatest average molecular speed at STP? (A) H2 (B) He (C) N2 (D) all are the same 9. Which of the following gases has the greatest density (g/l) at STP? (A) H2 (B) He (C) N2 (D) all are the same 10. Which of the following gases has the greatest concentration (mol/l) at STP? (A) H2 (B) He (C) N2 (D) all are the same 11. List at least two similarities and two differences between an ideal gas and a real gas. 12. Which gas would you expect to exhibit more obvious non-ideal behavior, H2 or H2O? Explain your answer. 8
Chemistry 222, Rogue Community College Intermolecular Forces Homework (Ch. 15) Name 1. Which of the following molecules exhibits hydrogen bonding? (A) CH4 (B) PH3 (C) H2S (D) H2O 2. Which of the following are intermolecular forces? (A) dipole-dipole interactions (B) London forces (C) hydrogen bonding (D) all of the above 3. Which of the following will tend to increase intermolecular forces? (A) increased molecular weight (B) increased polarity (C) increased hydrogen bonding (D) all of the above 4. Choose the substance with the highest boiling point: (A) CH4 (B) NH3 (C) H2O (D) HF 5. Choose the substance with the highest boiling point: (A) F2 (B) Cl2 (C) Br2 (D) I2 6. Which state of matter has both definite shape and definite volume? (A) solid (B) liquid (C) gas (D) none 7. Which state of matter has neither definite shape nor definite volume? (A) solid (B) liquid (C) gas (D) none 8. Which state of matter has definite shape but not definite volume? (A) solid (B) liquid (C) gas (D) none 9
9. Can nonpolar molecules experience van der Waals forces? Why or why not? 10. Why does ice float on liquid water? Is this the expected behavior of most substances? Why or why not? 11. Why does water have a relatively high surface tension? 12. Why is glycerol so viscous? 13. Distinguish between the terms surface tension and capillary action. 14. Briefly explain why water's meniscus is curved upward while mercury's meniscus is curved downward (in glass containers). 10
Chemistry 222, Rogue Community College Condensed Phases Homework (Ch. 15) Name 1. Distinguish between crystalline solids and amorphous solids. Be accurate, concise and parallel! 2. Distinguish between metallic solids and ionic solids. Be accurate, concise and parallel! 3. Distinguish between the valence band and the conduction band in a semi-conductor. Be accurate, concise and parallel! 4. Distinguish between molecular solids and network covalent solids. Be accurate, concise and parallel! 5. Calculate the amount of heat required in order to transform 10.0 g of liquid water at 25 o C to 10.0 g of water vapor at 175 o C. (Look up the necessary constants in Tables 15.3 and 14.6.) 11
6. Describe the terms x-ray diffraction and unit cell. 7. How many atoms are there in a simple cubic unit cell? How many atoms are there in a bcc unit cell? How many atoms are there in a fcc unit cell? Note: In answering this question, you must take into account that any corner, face or edge atoms are actually shared between more than one unit cell!! 8. Why does it take longer to boil an egg in Grants Pass than in Brookings? Include the concepts of vapor pressure and atmospheric pressure in your answer. 9. On the following phase diagram for an unknown substance, clearly label the melting point, boiling point, triple point, critical temperature and critical pressure for the substance. Pressure P atm Temperature 12
Chemistry 222 Rogue Community College Colligative Properties I Homework (Ch. 16) Name 1. A solution is prepared by dissolving 10.0 g of (solid) naphthalene (C10H10) in 500.0 g of (liquid) chloroform (CHCl3). The resulting solution is liquid. Identify the solute and the solvent. 2. Calculate the molality of the solution from #1. 3. Calculate the mole fractions of C10H10 and CHCl3 in the solution from #1. 4. Calculate the mass percents of C10H10 and CHCl3 in the solution from #1. 5. Calculate the molarity of the solution from #1 if its density is 1.50 g/ml. 13
6. Determine the ideal van t Hoff i-factor for each of the following aqueous solutions, and then rank them in order of increasing osmotic pressure. 0.10 M sucrose (C12H22O11) 0.08 M NaCl 0.03 M MgCl2 7. Rank the solutions from #6 in order of increasing vapor pressure. 8. Rank the solutions from #6 in order of increasing boiling point. 9. Rank the solutions from #6 in order of increasing freezing point. 10. 10.0 g of an unknown sugar is dissolved in 100.0 ml of water and the resulting freezing point is determined to be 0.37 C. Calculate the molecular weight of the sugar, given that Kf for water is 1.86 C/m. 14
Chemistry 222 Rogue Community College Colligative Properties II Homework (Ch. 16) Name 1. Clearly state Henry s Law, and give an example. 2. Clearly state Raoult s Law, and give an example. 3. Sketch a graph of rate of condensation vs. time for a pure solvent and a solution, and use it to explain why the vapor pressure of a pure liquid always decreases when a nonvolatile solute is dissolved in it. 15
5. Sketch a phase diagram (P vs. T) for water and salt water, and use it to explain why the boiling point of a pure liquid always decreases when a nonvolatile solute is dissolved in it. 6. If a beaker of pure water and a beaker of diluted sea water are placed under a bell jar, what will happen to the water level in each of the beakers and why? 7. If pure water and diluted sea water are placed on opposite sides of a semipermeable membrane in a U-shaped glass tube, what will happen to the water level on each side of the membrane and why? 8. What is an azeotrope, and why is it important to consider azeotrope formation when performing a distillation? 16
Chemistry 222 - Rogue Community College Kinetics I Homework (Ch. 17) Name 1. Identify each of the following statements as TRUE or FALSE. Correct any false statements. (a) The rate of a reaction can be expressed as the rate of disappearance of its products or the rate of appearance of its reactants. (b) If a compound, C, decomposes to products by a first-order reaction (C pdts), then rate = d[c]/dt = k[c]. (c) For the reaction: a A + b B c C + d D, if a plot of [A] vs. time is a straight line, then the reaction is first-order in [A]. (Assume an excess of [B].) (d) For the reaction: a A + b B c C + d D, if a plot of ln [A] vs. time is a straight line, then the reaction is first-order in [A]. (Assume an excess of [B].) (e) For the reaction: a A + b B c C + d D, if a plot of 1/[A] vs. time is a straight line, then the reaction is first-order in [A]. (Assume an excess of [B].) (f) If the reaction: a A + b B c C + d D is zero-order in [A], then a plot of [A] vs. time will be a straight line with a negative slope. (Assume an excess of [B].) (g) If the reaction: a A + b B c C + d D is first-order in [A], then a plot of ln [A] vs. time will be a straight line with a negative slope. (Assume excess [B].) (h) If the reaction: a A + b B c C + d D is second-order in [A], then a plot of 1/[A] vs. time will be a straight line with a negative slope. (Assume excess [B].) 17
2. Given the following data, determine the rate law for the following reaction: 2 N2O5 (g) 4 NO2 (g) + O2 (g) [N2O5]o (M) Initial Rate (M/s) 0.10 1.8 x 10-5 0.20 3.6 x 10-5 0.30 5.4 x 10-5 3. Calculate the rate constant, k, and half-life, t1/2, for the reaction in #2. Be sure to include the correct number of significant figures and the appropriate units in your answer. 4. Given the following data, determine the rate law for the following reaction: 2 NO (g) + F2 (g) 2 NOF (g) [NO]o (M) [F2]o (M) Initial Rate (M/s) 0.10 0.10 2.1 x 10-3 0.10 0.20 4.2 x 10-3 0.20 0.10 8.4 x 10-3 5. Calculate the rate constant, k, for the reaction in #4. Be sure to include the correct number of significant figures and the appropriate units in your answer. 18
Chemistry 222 - Rogue Community College Kinetics II Homework (Ch. 18) Name 1. If the following first-order reaction has a rate constant of 1.4 x 10 7 s 1, calculate the time required for [A]o = 0.175 M to reach [A] = 0.100 M. A + B C 2. The reaction 2 A + B C + D follows the rate law: rate = k[b] 2. The second-order rate constant is equal to 2.9 x 10 4 M 1 s 1. How long will it take for an original concentration, [B]o = 0.0500 M to reach 0.0400 M? 3. Identify all of the reactants, products, catalysts and intermediates in the following sequence of elementary steps for the oxidation of V 3+ to Fe 3+. Fe 3+ (aq) + Mn 2+ (aq) Fe 2+ (aq) + Mn 3+ (aq) Fe 3+ (aq) + Mn 3+ (aq) Fe 2+ (aq) + Mn 4+ (aq) V 3+ (aq) + Mn 4+ (aq) V 5+ (aq) + Mn 2+ (aq) 19
4. HCl reacts with propene, CH3CH=CH2 in the gas phase according to the overall reaction: HCl + CH3CH=CH2 CH3CHClCH3. The measure rate law is d[ch3ch=ch2]/dt = k[hcl] 3 [CH3CH=CH2]. Which, if any, of the following mechanisms is/are consistent with the observed rate law? (a) HCl + HCl H + HCl2 fast H + CH3CH=CH2 CH3CHCH3 slow HCl2 + CH3CHCH3 CH3CHClCH3 + HCl fast (b) HCl + HCl H2Cl2 fast HCl + CH3CH=CH2 CH3CHClCH3 * fast CH3CHClCH3 * + H2Cl2 CH3CHClCH3 + 2 HCl slow (c) HCl + CH3CH=CH2 H + CH3CHClCH2 fast H + HCl H2Cl fast H2Cl + CH3CHClCH2 CH3CHClCH3 + HCl slow 5. The following reaction mechanism has been proposed for a chemical reaction: A2 A + A fast A + B AB slow AB + CD AC + BD fast (a) Write a balanced equation for the overall reaction (b) Write a rate law that corresponds to the mechanism above. Express the rate in terms of concentrations of reactants only. 6. If the rate constant for a chemical reaction is 5.5 x 10 2 s -1 at 250 K, calculate the value of the rate constant at 350 K. The activation energy for the reaction is 475 J/mol. 7. If the rate constant for a chemical reaction is 8.9 x 10 5 M -1 s -1 at 25.0 C and 9.9 x 10 5 M -1 s -1 at 50.0 C, calculate the value of the rate constant at 100.0 C. What is the activation energy for this reaction? 20
Chemistry 222 - Rogue Community College Equilibrium I Homework (Ch. 19) Name 1. Write an equilibrium constant expression (K) for each of the following reactions. Use partial pressures for all gases and concentrations for all solutes. (a) CaCO3 (s) Ca 2+ (aq) + CO3 2 (aq) (b) CaCO3 (s) CaO (s) + CO2 (g) (c) 2 KClO3 (s) 2 KCl (s) + 3 O2 (g) (d) 2 HgO (s) 2 Hg (liq) + O2 (g) (e) 2 Hg (liq) + O2 (g) 2 HgO (s) (f) HgO (s) Hg (liq) + 1 O2 (g) 2 21
2. Consider the following equilibrium: N 2 (g) + 3 H 2 (g) 2 NH 3 (g) Once equilibrium is achieved at room temperature, the concentrations of the gases are measured and found to be (in moles per liter): [N 2 ] = 5.0 x 10-4, [H 2 ] = 1.0 x 10-3, and [NH 3 ] = 2.0 x 10-3. Calculate the value of the equilibrium constant (Kc) at room temperature. Watch significant figures! 3. For the reaction in #2, calculate the numerical value of the equilibrium constant (Kp) at room temperature given the following equilibrium partial pressures. Watch significant figures! P(N 2 ) = 0.0183 atm P(H 2 ) = 0.101 atm P(NH 3 ) = 0.500 atm 4. Are your answers to #2 and #3 consistent with the relationship Kp = Kc(RT)? Explain. 5. What is Kp at room temperature for 2 NH3 (g) N2 (g) + 3 H2 (g)? 22
Chemistry 222 - Rogue Community College Equilibrium II Homework (Ch. 19) Name The equilibrium constant (Kp) for the reaction H2 (g) + I2 (g) is 3.1 x 10 3 at 430 C. 2 HI (g) 1. Starting with 0.100 atm HI (g) only, what will be the equilibrium partial pressures of H2, I2 and HI? 2. Starting with 0.0100 atm H2 and 0.0100 atm I2 only, what will be the equilibrium partial pressures of H2, I2 and HI? 3. Starting with 0.0100 atm H2, 0.0500 atm I2 and 0.100 atm HI, (a) calculate the reaction quotient, Q (b) which way will the reaction proceed, to the left or to the right? (c) calculate the equilibrium partial pressures of H2, I2 and HI. 23
4. For the following reaction, determine the effect of each of the following changes on both the rate of reaction and the equilibrium position. Include a brief explanation of your reasoning. N 2 (g) + 3 H 2 (g) 2 NH 3 (g) + 22.1 kcal/mol increase in temperature: RATE OF REACTION increase decrease no change EQUILIBRIUM SHIFT right left no shift increase in pressure/decrease in volume: RATE OF REACTION increase decrease no change EQUILIBRIUM SHIFT right left no shift increase in [H 2 ]: RATE OF REACTION increase decrease no change EQUILIBRIUM SHIFT right left no shift increase in [NH 3 ]: RATE OF REACTION increase decrease no change EQUILIBRIUM SHIFT right left no shift addition of a catalyst: RATE OF REACTION increase decrease no change EQUILIBRIUM SHIFT right left no shift 24
Chemistry 222 - Rogue Community College Acids & Bases I Homework (Ch. 20) Name 1. Write the formula for the conjugate base of each of the following acids: HC 2 H 3 O 2 H 2 O HCO3 H 3 PO 4 NH4 + H3O + 2. Write the formula for the conjugate acid of each of the following bases: NH 3 H 2 O HCO3 F PO4 3 OH 3. Calculate the ph, poh and [OH ] of a solution with [H3O + ] = 1.7 x 10 4 M. (Watch significant figures! In ph and poh, only the digits to the right of the decimal point are significant!) 4. Calculate the [H3O + ], [OH ] and poh of a solution with ph = 10.53. Watch sig. figures! 25
5. Distinguish between the terms strong acid and weak acid, and give an example of each. 6. Distinguish between the terms strong base and weak base, and give an example of each. 7. If the Ka for acetic acid (CH3COOH) is 1.8 x 10 5, what is the Kb for acetate ion (CH3COO )? Show your work. 8. Calculate the ph of 0.100 M HCl. 9. Calculate the ph of 0.100 M acetic acid (CH3COOH) with Ka = 1.8 x 10 5. 10. Calculate the ph of 0.0500 M ammonia (NH3) with Kb = 1.8 x 10 5. 26
Chemistry 222 - Rogue Community College Acids & Bases II Homework (Ch. 20) Name 1. Calculate the ph and equilibrium concentrations ([H2CO3], [HCO3 ] and [CO3 2 ]) for a 0.0750 M solution of carbonic acid. Ionization constants can be found in Table 15.6. 2. Calculate the ph and equilibrium concentrations ([H2SO4], [HSO4 ] and [SO4 2 ]) for a 0.0150 M solution of sulfuric acid. 3. Calculate the ph and equilibrium concentrations ([H3PO4], [H2PO4 ], [HPO4 2 ] and [PO4 3 ]) for a 0.0325 M solution of phosphoric acid. 27
4. Without looking them up, and based on chemical reasoning, choose the stronger acid from each of the following pairs. (Circle your answers.) HClO3 or HClO4 HNO3 or H3PO4 H2PO4 or HPO4 2 5. Write the formula for each of the following compounds, and predict whether it will produce an acidic, basic or neutral solution. (Circle your answers.) sodium chloride: acidic basic neutral ammonium chloride: acidic basic neutral magnesium oxide: acidic basic neutral carbon dioxide: acidic basic neutral sulfur dioxide: acidic basic neutral diphosphorus pentoxide: acidic basic neutral potassium oxide: acidic basic neutral aluminum chloride: acidic basic neutral potassium cyanide: acidic basic neutral ammonium sulfate: acidic basic neutral ammonium acetate: acidic basic neutral ammonium carbonate: acidic basic neutral 6. Distinguish between the terms Lewis acid and Lewis base. 7. Identify the Lewis acid and the Lewis base in each of the following reactions: BF3 (g) + NH3 (g) BF3NH3 (s) H2O (l) + CO2 (g) H2CO3 (aq) Al 3+ (aq) + 6 H2O (l) Al(H2O)6 3+ 28