M = Molar mass ; m = mass; n = m/m

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Shanon Quinn
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1 AP Chem Unit 6 and 7 Review Name Know: characteristics of gases (KMT; gas laws-boyle, Charles, Avogadro, combined, ideal gas, partial pressure, density; effusion/diffusion; non-ideal behavior) gas stoichiometry (mole ratio; PV=nRT; molar mass) Intermolecular forces (types-ion-dipole, H-bonding, dipole, London; size/shape vs IMF; surface tension; viscosity; capillary action) States of matter (phase changes; heat of fusion; heat of vaporization; vapor pressure; phase diagrams) Solids (amorphous; crystalline-molecular, ionic, metallic, covalent network; cubic unit cells; lattice energy; close packing system) Solutions (formation; solubility factors-imf, pressure, temp; types of solutions-unsaturated, saturated, supersaturated; concentration-mass %,, mole fraction, molarity) g of hexane is placed in a steel cylinder. What is the pressure of the hexane vapor if the cylinder has a volume of 250. cm 3 and the temperature is 250 o C? 1.50g x (1mol/86.20g) = mol PV=nRT P(0.250) = (0.0174)(0.0821)(523) P = 2.98atm 2. When an evacuated 63.8 ml glass bulb is filled with a gas at 22 o C and 747 mm Hg, the bulb gains g in mass. Is the gas N 2, Ne, or Ar? PV = nrt (747)(0.0638)=n(62.4)(295) n = mol molar mass = 0.103g/ mol =39.78g/mol, Argon 3. Magnesium can be used as a getter in evacuated enclosures, to react with the last traces of oxygen. (The magnesium is usually heated by passing an electric current through a wire or a ribbon of the metal.) If an enclosure of L has a partial pressure of O 2 of 6.5 x 10-6 mm Hg at 27 o C, what mass of magnesium will react according to the following equation? 2Mg(s) + O 2 (g) à 2MgO(s) (6.5 x 10-6 mm Hg x (1 atm./760 mm Hg) = x 10-9 (8.553x10-9 )(0.283) = n(0.0821)(300.) n=9.8x10-11 mol O2 x (2mol Mg/1mol O2) x 24.31g/1mol) = 4.8x10-9 g 4. Consider two identical flasks: Flask A contains H 2 at 0 o C and 1.0 atm. Flask B contains CO 2 at 0 o C and 2.0 atm. Compare these two gases with respect to: a. Average kinetic energy per molecule. same because the temperature is the same, and temperature is proportional to kinetic energy b. Average molecular velocity. H 2 faster because H2 are lighter molecules, and if kinetic energy is the same, if mass is smaller then velocity is greater, because KE = 1/2mv 2 c. Number of molecules. more molecules of CO2 because higher pressure, and pressure is proportional to number of moles if volume and temp are the same. (PV=nRT) d. Mass of gas. CO2 is heavier because a larger molar mass and more molecules

2 5. Which represents the higher pressure in each of the following? a. a. 534 mm Hg or atm (1atm=760mmHg) b. 534 torr or 650 kpa (760torr = kPa) c atm or 9.34 kpa (1atm = kPa) 6. A sample of nitrogen gas has a pressure of 67.5 mm Hg in a 500. ml flask. What is the pressure when it is transferred to a 125 ml flask at the same temperature? P 1V 1 = P2 V2 (67.5)(500.) = P2 (125) P 2 = 270. mmhg 7. A 5.0 ml sample of CO 2 is enclosed in a gas tight syringe at 22 o C. If the syringe is immersed in an ice bath at 0 o C, What is the new volume if pressure is held constant? V 1/T1 = V2/T2 (5.0)/(295) = (V2)/(273) V 2 = 4.6mL 8. A helium filled balloon of the type used in long distance flying contains 1.20 x 10 5 L of helium, on the ground where the pressure is 737 mm Hg and the temperature is 16.0 o C. When the balloon ascends to a height of 2 miles, the pressure is 600. mm Hg, and the temperature is o C, what volume is occupied by the helium gas? P 1V 1/T1 = P2V 2/T2 (737)(1.2x10 5 )/289.0 = (600.)V2/240.0 V 2 = 1.22x10 5 L 9. Ethane is burned according to the following equation: C 2 H 6 (g) + 7O 2 (g) à 4CO 2 (g) + 6H 2 O(g) What volume of O 2 in liters, is required for complete reaction with 5.2 L of ethane? What volume of water vapor would be produced? All gases are measured at the same temperature and pressure. STP, therefore 22.4L/mol Volume O2: 5.2L x (1mol/22.4L) x (7mol O2/1mol ethane) x (22.4L/1mol) = 36L O2 Volume H2O: 5.2L x (1mol/22.4L) x (6mol H2O/1mol ethane) x (22.4L/mol) = 31L H2O 10. A balloon used in long distance flying contains 1.2 x 10 7 L of helium, on the ground where the pressure is 737 mm Hg and the temperature is 25.0 o C. What is the mass of the helium in the balloon? PV=nRT (737)(1.2x10 7 ) = n(62.4)(298) n = 4.76x10 5 mol He x (4.00g/1mol) = 1.9x10 6 g He 11. Diethyl ether (C 2 H 5 ) 2 O, vaporizes easily at room temperature. If the vapor is at a pressure of 233 torr, in a flask at 25.0 o C, what is the density of the vapor? Density = mass/v M = Molar mass ; m = mass; n = m/m PV=nRT, so PV = (m/m)xrt; after algebraic manipulation PM/RT=m/V; D=MP/RT D=MP/RT D = (74.14)(233)/[(62.4)(298)] D = 0.929g/L

3 12. Acetylene, C 2 H 2, can be made by allowing calcium carbide to react with water; CaC 2 (s) + 2H 2 O(l) à C 2 H 2 (g) + Ca(OH) 2 (s) Suppose you react 2.65 g of CaC 2 with excess water. If you collect the acetylene by water displacement and find that the gas has a volume of 795 ml at 27 o C and torr, what is the percent yield of acetylene? The vapor pressure of water at 27 o C is 26.7 torr. Percent yield = actual yield in grams/theoretical yield in grams Theoretical yield: 2.65g CaC2 x (1mol/64.09g) x (1mol C2H 2/1mol CaC2) x (26.04g/mol) = 1.041g (theoretical) 735.2torr-26.7torr = torr x 1 atm/760 torr = atm PV = nrt (0.9322)(0.795) = n (0.0821)(300.) n = mol x (26.04g/1mol) = 0.784g (actual) % yield = actual/theoretical x 100 = 0.784/1.041 x 100 = 75.3% yield 13. Equal masses of gaseous N 2 and Ar are placed in separate flasks of equal volume at the same temperature. Tell whether each of the following statements is true or false. Explain your answer. a. More molecules of N2 are present than atoms of Ar. True. Masses are equal, but because the molar mass of Ar is larger there are fewer moles of Ar therefore fewer molecules. b. The pressure is greater in the Ar flask. False. PV= nrt, so P= nrt/v. If T and V are the same, P is proportional to number of moles. If the number of moles of N2 is greater, the pressure is greater in the N2 flask. c. Ar atoms have a greater average speed than the N2 molecules. False, Ar atoms are larger and therefore have a slower average speed. KE = ½ mv 2. Since T is the same, KE is the same, and since mass and velocity are inversely proportional, the gas with the higher mass will have the lower speed. d. The molecules of N2 collide more frequently with the walls of the flask than do the atoms of Ar. True. There are more N2 molecules which are going faster than the Ar molecules so there are more collisions 14. Us e kinetic molecular theory to explain Charles law, Boyle s law. Charles Law: As temperature increases the molecules move faster therefore there are more collisions which increases the pressure. You must increase the volume in order to keep the pressure constant Boyle s Law: As volume decreases the molecules move closer together therefore there are more collisions and the pressure increases 15. What assumptions are made in describing an ideal gas? Under what circumstances is the ideal gas law least accurate? For an ideal gas it is assumed that there are elastic collisions between molecules (there are no IMF!!) and that the molecules have negligible/no volume. The ideal gas law is therefore less accurate with large molecules, high pressures and low temperatures. 16. Which of the following would you expect to be more soluble in water? Explain. a. a. CH 3 CH 2 OH or CH 3 CH 2 CH 2 CH 2 OH ethanol (CH 3 CH 2 OH )because smaller so Hydrogen bonding in ethanol is more prevalent hydrogen bonding in butanol, which has a longer nonpolar CH chain. The stronger the IMF formed by a substance with water, the more soluble it will be. b. b. BaSO 4 or NaCl BaSO4, because the ion-dipole IMF will be proportional to the charge product, according to Couloumb s law, (F is poroportional to charge and inversely proportional to distance.). The charge on the Ba ion and SO4 ion are both greater than Na+1 and Cl-1, so Ba+2 and SO4-2 will create a greater ion-dipole force with the water. While Na+1 and Cl-1 are smaller, charge will contribute more to the IMF force than distance. The stronger the IMF formed by a substance with water, the more soluble it will be.

4 c. c. CH 3 CH 2 OH or CH 3 CH 2 SH Ethanol because the oxygen and hydrogen will form hydgrogen bonds with the water molecules, which are stronger IMFs than the dipole Dipole forces that will beformed by the CH 3 CH 2 SH. The stronger the IMF formed by a substance with water, the more soluble it will be. 17. In each of the following groups of substances, pick the one that has the given property. Justify each answer. a. Highest boiling point: Hg, NaCl, or N2 Hg, metallic bonds are stronger than ionic bonds or London dispersion forces b. Smallest surface tension: H2O, CH3CN, or CH3OH CH3CN, all others have H-bonding with each other, so CH3CN has the weakest IMF. Surface tension is related to how strong the IMFs are holding the molecules together. c. Lowest freezing point: H2, CH4, or CO.H2 because it has the weakest IMF (London Dispersion Forces it is non polar and smaller than H4). With very weak IMF, the molecules have very little attraction for eachother and must slow down substantially before they become a solid. CO is, polar so it has stronger IMF and will have the highest freezing/melting oint. Smallest vapor pressure at 25 C: SiO2, CO2, H2O H 2O, H-bonding so stronger IMF than nonpolar SiO2 and CO2. However, SiO2 is a covalent network solid at STP so it would have the strongest IMF forces (covalent bonds) and the true lowest vapor pressure. d. Greatest viscosity: CH3CH2CH2CH3, CH3CH2OH, or HOCH2CH2OH HOCH2CH2OH, more OH so more IMF than ethanol and butane (nonpolar) e. Strongest hydrogen bond: NH3, PH3, or SbH3 NH3 because hydrogen bonds are only formed when hydrogen is bonded to Nitrogen, oxygen or fluorine. This is because nitrogen, oxygen and fluorine are so electrobegative. Remember a hydrogen bond is really an intermolecular force between the hydrogen in one molecule (that is bonded to an O, N or F) and the O, N or F in another (that is bonded to an H). You will have to draw a hydrogen bond on the quiz. f. Greatest heat of vaporization: HF, HCl, HBr, or HI g. Smallest enthalpy of fusion: H 2 O, CO 2, MgO, or Li 2 O 18. How do the following physical properties depend on the strength of intermolecular forces? a. Surface tension b. Viscosity c. Melting point d. Boiling point e. Vapor Pressure f. Heat of vaporization. Surface tension stronger IMF higher surface tension, because with stronger IMF, the molecules are more strongly attraced to each other. b. Viscosity: stronger IMF higher viscosity, because with stonger IMF, the molecules are more strongly attracted to each other. c. Melting point: stronger IMF, higher melting point, because with stronger IMF, the molecules are more stongly attracted to each other. It thereore will take more energy to separate them from a solid state to a liquid state. d. Boiling point stronger IMF higher BP e. Vapor Pressure stronger IMF lower vapor pressure f. Heat of vaporization for the same reason as the p;revious statement. stronger IMF higher heat of vaporization 19. Predict which substances in each of the following pairs would have the greater dipole-dipole forces. a. CO 2 or OCS b. PF 3 or PF 5 c. SO 3 or SO 2 WILL POST ANSWER LATER 20. For which of the following pairs would you expect the hydrogen bonding to be greater? a. B(OH) 3 or BH 3 b. CH 3 OH or H 2 CO c. HF or HI WILL POST ANSWER LATER 21. Rationalize the difference in boiling points for each of the following pairs of substances: a. HF 20 o C b. HCl -85 o C c. LiCl 1360 o C HCl -85 o C LiCl 1360 o C CsCl 1290 o C

5 22. The enthalpy of vaporization of acetone,c 3 H 6 O, is32.0 kj/mol. The normal boiling point is 56.5 o C. The specific heat capacity is 2.15 J/g o C. How much energy would be required to raise the temperature of 10.00g of acetone from 25.0 o C to its boiling point, and vaporize the entire sample? 27. What type of solid will each of the following substances form? a. CO 2 b. SiO 2 c. KBr d. H 2 O e. U 28. dentify the type of solid each of the following substances would form.: a. BaSO4 b. H2S c. Xe ionic molecular molecular d. C2H6 e. Cs f. Hg molecular metallic metallic g. P4 h. NH4Cl i. HCl covalent network molecular molecular 29. Sodium chloride (NaCl), Calcium chloride (CaCl 2 ), and a non-electrolyte urea CO(NH 2) are frequently used to melt ice on streets. Rank these from high to low in terms of effectiveness per mole in lowering the freezing point. Explain your answer. This will not be on the quiz. I have not taught it yet.

g of CO 2 gas is at a temperature of 45 o C and a pressure of 125 kpa. What is the volume of the container? 11 L

g of CO 2 gas is at a temperature of 45 o C and a pressure of 125 kpa. What is the volume of the container? 11 L Name period AP Chemistry Unit 5 answers 1. A fixed quantity of gas at 23⁰C exhibits a pressure of 748 torr and occupies a volume of 10.3 L. Calculate the volume the gas will occupy if the temperature is