AP CHEMISTRY MIDTERM REVIEW CHAPTER 4 REVIEW 1. Write the balanced net ionic equation: H2SO4 + CaCO3 CaSO4 + H2O + CO2 2 H+ + CO32- H2O + CO2 2. Balance the following redox reaction: MnO2 +4 HBr MnBr2 + 2 H2O + Br2 3. Balance the following redox reaction: 8 I- + SO42- + 10 H+ 4 I2 + H2S + 4 H2O 4. Balance the following reaction in basic aqueous solution: 5 H2O + 3 SO32- + 2 CrO42- 3 SO42- + 2 Cr(OH)3 + 4 OH- CHAPTER 5 REVIEW 1. Which of the following gases diffuses 4 times faster than C6H8Br3 a. He b. Ar c. Ne (MM of 20) d. O3 e. other 4 = √ ( 320 ) and then x = 20 1 x 2. Calculate the partial pressure of CO in a CO/CO2 mixture if the mole fraction of CO2 is 0.450 and the total pressure is 3.00 atmosphere. XCO = 1 -0.45 = 0.55 so 0.55 = y 1 3 atm so y = 1.65 atm 3. If 200.0 mL of O2 were collected over H2O at 27C and 727 torr, calculate the volume of dry O2 at STP. The vapor pressure of H2O at 27C is 27 torr. 727 – 27 = 700 torr and 700 (200) = 760 (V2) 300 273 so V2 = 168 mL 4. Which of the following diffuses at the same rate as CO? a. CH4 b. C2H4 c. C3H8 d. H2CO e. none Since CO = 28 g/mol it will be C2H4 because it is also 28 g/mol 5. If 500.0 mL of a gas at 127C was cooled to -73C at constant pressure, what would be the final volume of the gas? 500 = V 400 200 so v = 250 mL 6. If 2.20 g of CO2 exerts a pressure of 700. torr at 73C, what pressure would 13.2 g of CO2 exert in the same container at 73C? 4200 torr 7. If 400.0 mL of H2 at 730. torr was subjected to a pressure of 2.50 atmospheres, what would be the final volume of H2 assuming constant temperature? 154 mL 8. A certain gas occupies a volume of 100 mL at a temperature of 20C. What will its volume be at 10C, if the pressure remains constant? 96.6 mL 9. Calculate the pressure required to compress 2 liters of a gas at 700 mm pressure and 20C into a container of 0.1 liter capacity at a temperature of -150C? 5877 mm 10. A flask containing H2 at 0C was sealed off at a pressure of 1 atm and the gas was found to weigh, 4512 g. Calculate the number of moles and the number of molecules of H2 present. 2256 mol and 1.36 x 1027 molecules 11. Using van der waal’s equation, calculate the pressure exerted by 1 mole of carbon dioxide at 0c in a volume of a) 1.00 liter , and b) 0.05 liter a = 3.59 L2 atm/mol2 b= 0.0427 L/mol 1.98 atm and 1632 atm 12. Of the following two pairs, which member will more likely deviate from ideal gas behavior? (1) N2 versus CO (2) CH4 versus C2H6 13. What is the partial pressure of each gas in a mixture which contains 40 g He, 56 g N2, and 16 g O2, if the total pressure of the mixture is 5 atmospheres. 4 atm He, 0.8 atm N2 and 0.2 atm O2 14. At standard conditions, 1 liter of oxygen gas weighs almost 1.44 g, whereas 1 liter of hydrogen weighs only 0.09 g. Which gas diffuses faster? Calculate how much faster. H2 4 times faster 15. The root mean square (rms) speed of hydrogen (H2) at a fixed temperature, T, is 1600 m/sec. What is the rms speed of oxygen (O2) at the same temperature? 1600/4 = 400 m/s Chapters 6 and 16 Review 1. Calculate the quantity of heat required to raise the temperature of 3.78 liters (H2O should have been written in there sorry) from 10C and 80C. q = 4.18 (3780 g) (70) = 1106028 J or 1106 kJ 2. A piece of iron weighing 20.0 g at a temperature of 95.0C was placed in 100.0 g of water at 25.0C. Assuming that no heat is lost to the surroundings, what is the resulting temperature of the iron and water? Specific heat: iron = .108 cal/gC and water = 1.0 cal/gC Tf = 26.47 C 3. Determine H for the following reaction of burning ethyl alcohol in oxygen: C2H5OH (l) + 3 O2 (g) 2 CO2 (g) + 3 H2O (l) Hf of C2H5OH = - 65.9 kcal/mol Hf of CO2 = -94.1 kcal/mol Hf of H2O = -68.3 kcal/mol H = -327.2 kcal 4. Given the following reactions: S (S) + O2 (g) SO2 (g) SO2 (g) + ½ O2 (g) SO3 (g) Calculate H for the reaction: H = -94.5 kcal H = -71.0 kcal H = -23.5 kcal S (s) + 3/2 O2 (g) SO3 (g) 5. Calculate the standard enthalpy change, H, for the combustion of ammonia, NH3 (g), to give nitric oxide, NO (g), and water H2O (l). The enthalpies of formation, Hf, are –68.32 kcal/mol for water, -11.02 kcal/mol for ammonia, and 21.37 kcal/mol for nitric oxide. -140.18 kcal/mol 6. Calculate the quantity of heat required to (a) convert a liter of water at 30C to a liter of water at 60C, and (b) heat a 1 kg block of aluminum from 30C to 60C. Assume the specific heat of water = 1 cal/gC and aluminum = .215 cal/gC. 30 kcal for water and 6.45 kcal for Al 7. A chemist expands an ideal gas against a constant external pressure of 700 mm Hg, and finds its volume changes from 50 to 150 liters. He finds that 1.55 kcal of heat have been absorbed in the process. Determine the internal energy change that took place. 24.217 cal = 1 L atm Remember that E = q + w (w = -pV) solve for q. q = +3.78 kcal 8. Exactly one mole of gaseous methane is oxidized at fixed volume and at 25C according to the reaction CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l) If 212 kcal is liberated, what is the change in enthalpy? H = -212 kcal/mol (negative because it is liberated or given off) 9. 40 g of ice at 0C is mixed with 100 g of water at 60C. What is the final temperature after equilibrium has been established? Heat of fusion of water = 80 cal/g and specific heat = 1 cal/gC (qmelting ice + qwarming ice water = Tf = 20 C - qcooling hot water) 10. Calculate S for the conversion of one mole of liquid water to vapor at 100C. Heat of vaporization = 540 cal/g. 18 g/mol (540 cal/g) = 9720 cal/mol 11. A chemist knows that the H = 485 kJ for the reaction 2H2 (g) + O2 (g) 2 H2O (g) and that H = -537 kJ for H2 (g) + F2 (g) 2 HF (g). With this information, he calculated the H for 2 H2O (g) + 2 F2 (g) 4 HF (g) + O2 (g) and predicted whether S was positive or negative. How? H = -1559 kJ and S is positive more moles produced increasing disorder 12. Determine G for the reaction 4 NH3 (g) + 5 O2 (g) 4 NO Gf of NH3 = -4.0 kcal/mol Gf of NO = 20.7 kcal/mol Gf of H2O = -56.7 kcal/mol -241.4 kcal (g) + 6 H2O (l) 13. Calculate the equilibrium constant for the following reaction at 25C C (graphite) + 2 H2 (g) CH4 (g) H for this reaction is –17,889 cal NOT ENOUGH INFORMATION LOOKED UP VALUES IN TEXT H - T S = G = - RT ln k -75 – 298 (0.186) = -130 = -R (298) ln K and k = 1.054 14. If the standard free energy of formation of HI from H2 and I2 at 490C is –12.1 kJ/mol of HI, what is the equilibrium constant for this reaction? k = 1.00 CHAPTER 7 REVIEW (no questions provided but you still need to study this material) CHAPTER 8 1. What is the explanation for the following trends in lattice energies? NaF = 260 kcal/mol NaCl = 186 kcal/mol NaCl = 186 kcal/mol KCl = 169 kcal/mol NaBr = 177 kcal/mol CsCl = 156 kcal/mol As the size of atoms increase the bond strength between atom decreases. 2. Which molecule of each of the following pairs would exhibit a higher degree of polarity. HCl and HBr, H2O and H2S; BrCl and IF ? 3. Of the following pairs, which member should exhibit the largest dipole moment. Use the electronegativity table. (a) H-O and H-N; (b) H-F and H-Br; (c) C-O and C-S. 4. You are given H, N, O, Ne, Ca, Al, and Zn. Determine which of these atoms (in their ground state) are likely to be paramagnetic. Arrange these elements in the order of increasing paramagnetism. 5. Compare the bond order of He2 and He2+. 6. Which of the following could be the quantum numbers (n,l,ml,ms) electron in a potassium atom in its ground state? a. 3,0,0, ½ b. 3,1,1, ½ c. 4,0,0, ½ d. 7. Which of the following elements is diamagnetic? a. H b. Li c. Be d. B e. C 8. Which of the following could be the quantum numbers (n,l,ml,ms) electron in a phosphorus atom? a. 2,0,0, ½ b. 3,4,1, ½ c. 2,1,0, ½ d. 9. Which of the following ions has the smallest ionic radius? a. O2b. Fc. Na+ d. Mg2+ e. Al3+ for the valence 4,1,1, ½ for the valence 3,1,1, ½ CHAPTER 11 REVIEW 1. Calculate the mole fractions of C2H5OH, and water in a solution made by dissolving 9.2 g of alcohol in 18 g of water. XH2O = 0.833 2. By how much will 50. grams of water have its freezing point depressed if you add 30. grams of glucose (C6H12O6) to it? 6.21 C 3. Calculate the molality of an alcohol-water mixture which will not freeze above a temperature of -10C. (MW of alcohol = 46.0; Kf for water = 1.86C) 5.37 mol/kg 4. The molal freezing point constant for a certain liquid is 0.500C. 26.4 g of a solute dissolved in 250 g of this liquid yields a solution which has a freezing point 0.125 below that of the pure liquid. Calculate the molecular weight of this solute. MW = 422.4 g/mol (which seems really high to me) 5. What is the approximate boiling point at standard pressure of a solution prepared by dissolving 234 g of NaCl in 500 g of water? 106.09C after you add 6.09C to 100C. 6. Ethanol boils at 78.5C. If 10 g of sucrose (C12H2O11) is dissolved in 150 g of ethanol, at what temperature will the solution boil? Assume Kb = 1.20C/M for the alcohol. 78.7 C after you add the 0.2C to 78.5C 7. The vapor pressures of pure benzene and toluene at 60C are 385 and 139 Torr, respectively. Calculate (a) the partial pressures of benzene and toluene, (b) the total vapor pressure of the solution, and (c) the mole fraction of toluene in the vapor above a solution with 0.60 mole fraction toluene. a. 83.4 torr Benzene and 154 torr toluene b. 237.4 torr c. XB = 0.351 and XT = 0.649 8. A solution of 20.0 g of a non-volatile solute in 100 g of benzene at 30C has a vapor pressure 13.4 torr lower than the vapor pressure of pure benzene. What is the mole fraction of solute? Vapor pressure of benzene at 30C = 121.8 torr. Xsol = 0.11 9. The vapor pressure of benzene at 75C is 640 torr. A solution of 3.68 g of a solute in 53.0 g benzene has a vapor pressure of 615 torr. Calculate the molecular weight of the solute. (MW of benzene = 78.0) MW = 136 g 10. A sugar solution was prepared by dissolving 9.0 g of sugar in 500 g of water. At 27C, the osmotic pressure was measured as 2.46 atm. Determine the molecular weight of the sugar. Using π = MRT and therefore Molarity = 0.0999 mol/L therefore MW = 180 g 11. Determine the mass of water to which 293 g of NaCl is added to obtain a 0.25 molal solution. 20.05 kg 12. Calculate the normality of a solution containing 2.45 g of sulfuric acid in 2.00 liters of solution. 0.025 mol H+/mol AP Chemistry Midterm Review Problems 1. __3___ Fe + __4___ H2O _____ Fe3O4 + __4___ H2 a. Balance the equation. b. Calculate the formula weight for each of the four substances. 55.85, 18.02, 231.55, and 2.02 c. Assume that 100% of 42 available grams of iron react. Calculate the amounts in grams involved for the other three substances. 18.07, 58.04, 2.02 d. Assuming STP, calculate the volume of hydrogen gas produced from the 42 grams of iron. 22.4 L 2. Interpret each of the following four examples using modern bonding principles. a. C2H2 and C2H6 both contain two carbon atoms. However, the bond between the two carbons in C2H2 is significantly shorter than that between the two carbons in C 2H6. These carbons are triple bonded which contains one sigma and two pi bonds. b. The bond angle in the hydronium ion, H3O+, is less than 109.5, the angle of a tetrahedral. The lone pair of electrons on the Oxygen is more repulsive than the bonded electron pairs pushing the bonds closer together than the normal tetrahedral. c. The lengths of the bonds between the carbon and the oxygens in the carbonate ion, CO32-, are all equal and are longer than one might expect to find in the carbon monoxide molecule, CO. Carbonate has resonance 3 structures that allow the double bonds to move around. One is double bonded while 2 are single bonded, so the average length is between double and single (ex: If a single bond was 0.100 pm and double was .080 pm then 0.1(x2) + 0.08 /3 = 0.093 pm for average length) d. The CNO- ion is linear. O – C – N (the C-N bond is a triple bond, the oxygen has the extra electron and there are no lone pairs on the carbon to disrupt the linear shape.) 3. 2 H2 (g) + O2 (g) 2 H2O (l) The reaction above proceeds spontaneously from standard conditions at 298 K. a. Predict the sign of the entropy change, S, for the reaction. Explain. Negative, less moles and state of matter change is also less entropic b. How would the value of S for the reaction change if the product of the reaction was H2O (g)? still negative but closer to zero c. What is the sign of G at 298 K? Explain. Negative because it is a spontaneous reaction. d. What is the sign of H at 298 K? Explain. It must be in the realm of negative numbers in order for G to be negative. H must be more negative than the -TS term. Since S is negative then the -TS has a positive value and H must be a larger negative value. 4. CaO (s) + CO2 (g) CaCO3 (s) The reaction above is spontaneous at 298 K and the heat of reaction, H is –178 kJ a. Predict the sign of the entropy change, S, for the reaction. Explain. Negative, fewer moles and changing from gas to solid b. What is the sign of G at 298 K? Explain. Negative bc the reaction is spontaneous c. What change, if any, occurs to the value of G as the temperature is increased from 298 K? As T increase the –T S portion could become larger the H and change G to positive which would cause the reaction to be nonspontaneous and stop reacting d. As the reaction takes place in a closed container what changes will occur in the concentration of CO2 and the temperature? It should decrease as it is used to make the product. 5. Use your knowledge of chemical principles and the kinetic molecular theory to explain the following statements. a. A gasoline engine stops working effectively at very high altitudes. With a decrease in oxygen there would be fewer collision between particles required for combustion and thus the decrease in efficiency b. A glass of water left out in air can completely vaporize, even though the temperature never comes close to the boiling point of water. Molecules at the surface will break away because they have limited H – bonds directions and therefore it takes less energy to vaporize them than molecules within the liquid which have H – bonds in all directions. c. The volume of a gas filled balloon placed underwater at a constant temperature will decrease as its depth below the surface of the water is increased. The pressure increases upon the balloon as the depth increases and since Boyle’s Law says that pressure and volume are inversely proportional at constant temperature then the volume should decrease. d. As the temperature of the gas is decreased, the measured pressure of the gas becomes less than the pressure predicted by the ideal gas law. At low temperatures non-ideal gases will interact with the surface of the container and each other and then condensation will occur. These condensed particles (now liquid) will cause the pressure to drop below the expected value since they are no longer gases. 6. A gaseous hydrocarbon sample is completely burned in air, producing 1.80 liters of carbon dioxide at standard temperature and pressure and 2.16 grams of water. a. What is the empirical formula of the hydrocarbon? Convert volume to moles of CO2 and calculate moles of C in the CO2. All of this carbon started in the hydrocarbon. Use the mass of the water to calculate moles of water and then hydrogen. Determine the ratio between the C and H it should be a 1:3 ratio, so the formula is CH3 b. What is the mass of the hydrocarbon consumed? Convert the moles of carbon and hydrogen from previous part into masses and add together. Should be 1.2 g c. The hydrocarbon was initially contained in a closed 1.00 liter vessel at a temperature of 32C and a pressure of 760 mm Hg. What is the molecular formula of the hydrocarbon? Using these values and PV = nRT you can calculate the moles of hydrocarbon, then using the equation n = mass/MM you can solve for the MM as 30. Since CH3 has a mass of 15 the molecule must be twice as big, or C2H6. d. Write a balanced equation for the combustion of the hydrocarbon. 2 C2H6 + 7 O2 4 CO2 + 6 H2O 7. Use your knowledge of the periodic table to answer the following questions. a. Explain the trend in electronegativity from P to S to Cl. EN is inversely proportional to size, from P to Cl size decreases and therefore the EN values are increasing b. Explain the trend in electronegativity from Cl to Br to I. EN is inversely proportional to size, from Cl to I size increases and therefore the EN values are decreasing c. Explain the trend in atomic radius from Li to Na to K. Within a group size is dependent upon the number of energy levels being used by the electrons. Li only use 1 and 2 energy level while K uses 1, 2, 3, and 4 th energy levels, therefore the size increases going down the group. d. Explain the trend in atomic radius from Al to Mg to Na. These three elements are all within the same period and there valence electrons are on the 3rd energy level, which would put there electrons at approximately the same distance. However, the electrons are not the entire story because the number of protons in Al is 2 more than that of Na. These extra protons would pull aluminum’s 3rd energy level electrons in closer than Sodium would pull its electrons. So Al is the smallest and Na is the largest in this group. 8. A solution of sulfuric acid was made by dissolving 24.9 grams of H 2SO4 in 275 mL of water. The resulting volume was 280. mL. a. Calculate the density of the solution. = 0.089 g/mL b. Calculate the mole fraction. = XH2so4 = 0.016 and XH2O = 0.984 c. Calculate the molarity. = 0.907 M H2SO4 d. Calculate the molality. = 0.924 m H2SO4 e. Calculate the normality. = 1.814 N H+ f. Calculate the mass percent. 8.3 % H2SO4 and 91.7 % H2O