GENERAL CHEMISTRY II CHM202 Unit 1 Practice Test Solutions

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1 GENERAL CHEMISTRY II CHM202 Unit 1 Practice Test Solutions 1. Which one of the following substances is expected to have the highest boiling point? D) I2 Since these are all nonpolar ecules, the only interecular forces are dispersion forces. Polarizability is the only factor in play, so the largest (most diffuse) ecule with the most electrons will have the strongest interecular force and, therefore, the highest boiling point. 2. For which of the following species are the dispersion forces strongest? E) C8H18 Since these are all nonpolar ecules, the only interecular forces are dispersion forces. Polarizability is the only factor in play, so the largest (most diffuse) ecule with the most electrons will have the strongest interecular force 3. Which one of the following substances should exhibit hydrogen bonding in the liquid state? A) SiH 4 No small, highly electronegative atoms (N, O, F) are present. B) H 2 No small, highly electronegative atoms (N, O, F) are present. C) H 2S No small, highly electronegative atoms (N, O, F) are present. D) CH 4 No small, highly electronegative atoms (N, O, F) are present. E) CH3NH2 Nitrogen, a small, highly electronegative atom. is present and it is bonded to a hydrogen atom.. 4. The boiling points of propanol (CH 3CH 2CH 2OH) and pentanol (CH 3CH 2CH 2CH 2CH 2OH) are 97 C and 137 C, respectively. The boiling point of butanol (CH 3CH 2CH 2CH 2OH) is predicted to be: C) > 97 C and < 137 C The polarity of all three ecules should be approximately the same, so the dispersion forces make the difference. Larger ecules have greater dispersion forces. Since butanol s ar mass is between that of propanol and pentanol, the dispersion forces and the boiling points should also be. 5. Potassium crystallizes in a body-centered cubic lattice. How many atoms are there per unit cell? B) 2 8 corner atoms (8 X 1/8) plus one atom completely contained within the body of the cell (1 X 1). 6. Determine the normal boiling point of carbon disulfide, CS 2 from the graph below C) 48 C The normal bp is the temperature at which the vapor pressure is equal to standard atmospheric pressure, 760 mmhg. Reading the graph at that point shows a temperature at 760 mmhg of just under 50 C.

2 7. Based on the phase diagram shown below, how will the melting point of the substance change if the pressure is increased above 1 atm? C) The melting point will increase. P2 > P1 and T2 > T1, so the melting point increases. 8. Which property of a liquid refers to how freely it flows? A) viscosity By definition. 9. Which one of the following is an example of a covalent network solid? A) SiO2 Glass or quartz are examples of a covalent network.. B) K Metallic crystal C) I 2 Molecular crystal D) CaCl 2 Ionic crystal 10. Which of the following constants is/are needed to calculate the amount of energy required to convert an ice cube at -18 C to steam at 130 C? I. ΔH fus (H 2O) Enthalpy of phase change from solid to liquid (needed to calculate) II. ΔH vap (H 2O) Enthalpy from of phase change from liquid to gas (needed to calculate) III. specific heat of H 2O(s) Heat needed to raise the temperature of the solid (needed to calculate) IV. specific heat of H 2O(l) Heat needed to raise the temperature of the liquid (needed to calculate) V. specific heat of H 2O(g) Heat needed to raise the temperature of the gas (needed to calculate) E) I, II, III, IV and V

3 11. The normal boiling point of methanol (CH 3OH) is 64.6 C. Given that the vapor pressure of methanol is 75.0 torr at 15.2 C, calculate the ar enthalpy of vaporization of methanol. D) 38.0 kj/ As long as P1 corresponds to T1, etc., the naming of the data points is arbitrary. P atm (pressure at the normal bp); T C K P torr atm; T C K R l atm/ K ΔHvap? Using Clausius-Clapeyron: ln P 1 H vap P 2 R ( 1 T 2 1 T 1 ) ln 1.00atm.09868atm H vap 8.314J K ( ) ΔHvap J/ 38.0 kj/ (3 sf) H vap 8.314J K ( 1 1 ) K K 12. Select True or False: The freezing point of a liquid does not change as the atmospheric pressure changes. B) False See question # Calculate the ality of a solution containing 14.3 g of NaCl in 42.2 g of water. E) 5.80 m ality solute mass 14.3g M g/ kg ality 5.798m 5.80m (3 sf) 14. Which of the following compounds should be soluble in CCl 4? D) C8H18 CCl4 is nonpolar. The principle of like dissolves like indicated that only a nonpolar substance will dissolve. Of these, only octane is nonpolar. 15. The solubility of nitrogen gas at 25 C and a nitrogen pressure of 522 mmhg is /L. What is the value of the Henry's Law constant in /L atm? D) /L atm Solve Henry s Law, c kp, for the constant, k. k c P /L 522mmHg 760 mmhg/atm L atm L atm (3 sf)

4 16. The vapor pressure of water at 45.0 C is mmhg. Calculate the vapor pressure of a solution of 1.25m Al(ClO 3) 3 at this temperature (assume 100% dissociation). E) 66.0 mmhg Compute the e fraction of Al(ClO3)3, taking into account the van t Hoff factor of 4 (4 ions produced by 100% dissociation). X ( 1000g 18.01g ) Now apply Raoult s Law: P X 2 P mmHg mmHg P 1 P 1 0 P mmHg mmHg mmHg 66. 0mmHg (3 sf) You would get the same answer computing the e fraction of water and computing the pressure directly. 17. What is the osmotic pressure of a solution that contains 13.7 g of propyl alcohol (C 3H 7OH) (a nonelectrolyte) dissolved in enough water to make L of solution at 27 C? E) 11.2 atm Compute the arity of C3H7OH: M 13.7g g 0.500L Now the osmotic pressure: L M π MRT L atm L ( )K atm 11. 2atm (3 sf) K 18. When 24.0 g of glucose (a nonelectrolyte) is dissolved in kg of water, the solution has a freezing point of 0.47 C. What is the ar mass of glucose? K f of water is 1.86 C/m. E) 190 g/ Determine the ality from the freezing point depression: m glucose T f k f Now the es of glucose: 0 ( 0.47 ) m m n kg kg Now the ar mass: M mass n 24.0g g g (2 sf) 19. Which of the following aqueous solutions has the highest boiling point (assume 100% dissociation for all soluble ionic compounds)? A) 0.10m Al(NO 3) 3 (an electrolyte) (i 4) 0.10 x m B) 0.11m Na 2SO 4 (an electrolyte) (i 3) 0.11 x m C) 0.15m K2CO3 (an electrolyte) (i 3) 0.15 x m (this will cause the highest bp elevation) D) 0.18m NaCl (an electrolyte) (i 2) 0.18 x m E) 0.35m C 6H 12O 6 (not an electrolyte) (i 1) 0.35m

5 20. If 14.2 g of Al(NO 3) 3 is dissolved in 655g of water, what is the boiling point of the solution (assume 100% dissociation, K b (H 2O) 0.52 C/m)? D) C T b ik b m where i 4, k b m and m M Compute the concentration: m M 14.2g g 0.655kg Compute the boiling point elevation: m T b ik b m m m T b T b 0 + T b Calculate the freezing point of the coolant in an engine consisting of 2.5 kg of ethylene glycol (ar mass g/) and 6.7 kg of water. K f for water is 1.86 C/m. C) -11 C T f ik f m where i 1, k f mass solvent m and m M Compute the concentration: m M 2500g 62.07g 6.7kg Compute the boiling point elevation: m T b ik b m m m 11 (2 sf) T f T f 0 T f (0 decimal places) 22. Select True or False: A solution made of pentane and hexane has a e fraction, X of pentane. Hexane is the solute. B) False Since Xpentane + Xhexane 1 (all fractions of the whole must add up to one), Xhexane That s more than 0.25, so hexane is the solvent.

Chem 1100 Pre-Test 3. Multiple Choice Identify the choice that best completes the statement or answers the question.

Chem 1100 Pre-Test 3. Multiple Choice Identify the choice that best completes the statement or answers the question. Chem 1100 Pre-Test 3 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. An open-tube manometer is used to measure the pressure in a flask. The atmospheric