Ch 12 Solutions SG

7/24/2019 Ch 12 Solutions SG

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Chapter 14 1

Chapter 14 Solutions

14.1. You dissolve 1.0 mol of urea (H2N-CO-NH2) in 270 g of water. What is the mole fraction of urea?

1. 1.0 3. 16

2. 0.063 4. 3.7 x 10-3

14.2. You dissolve 92.0 grams of CH3CH2OH, ethanol, in 270 g of water. What is the mole fraction of

ethanol in the solution?

1. 2.0 3. 0.067

2. 0.12 4. 8.3

14.3. You dissolve 92.0 grams of CH3CH2OH, ethanol, in 270. g of water. What is the weight percent of


1. 34.1 % 3. 25.4 %

2. 17.0 % 4. 74.8 %

14.4. You dissolve 92.0 grams of CH3CH2OH, ethanol, in 270. g of water. What is the molality of


1. 341 m 3. 0.341 m

2. 170 m 4. 7.41 m

14.5. Given the heat of formation data below, calculate !solutionH for LiOH.

!fH [LiOH(s)] = -484.93 kJ/mol !fH [LiOH(aq)] = -508.48 kJ/mol

1. +23.55 kJ/mol 3. -23.55 kJ/mol

2. +993.41 kJ/mol 4. -993.41 kJ/mol

14.6. In which of the following solvents do you expect LiCl to be highly soluble?

1. H2O(liq) 3. CS2(liq)2. CCl4(liq) 4. CH3CH2CH2CH2CH3(liq)

14.7. Which of the following ions would you predict to have the most negative enthalpy of hydration?

1. Rb+ 3. Na+

3. Mg2+ 4. Ba2+

14.8. Which of the following changes in the property of a salt would increase its heat of solution (that is,

lead to a more negative enthalpy of solution)?

1. a decrease in lattice enthalpy

2. an increase in lattice enthalpy

3. a smaller (less negative) hydration energy for the cation4. a higher melting point

14.9. The enthalpy of solution of NH4NO3is +25.7 kJ/mol. A beaker contains 100. mL of a saturated

solution of NH4NO3at 25 C. The beaker has 52 grams of undissolved solid on the bottom. Which of

the following changes will cause some of the dissolved NH4NO3to precipitate?

1. remove 10. grams of the solid from the beaker

2. heat the solution by 10. degrees


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Chapter 14 2

3. cool the solution by 10. degrees

4. add 10. grams of additional NH4NO3solid

14.10. You have a saturated solution of NaCl at 25 C. No solid is present in the beaker. What could be

done to increase the amount of dissolved NaCl in this solution? (!solnH[NaCl] = +2.75 kJ/mol)

1. add some more solid NaCl2. raise the temperature of the solution

3. raise the temperature of the solution and add some NaCl

4. lower the temperature of the solution and add some NaCl

14.11. You dissolve 0.0400 mol of I2(10.1 g) in 1.96 mol of CCl4(300 g) at 65 C. Given that the vapor

pressure of pure CCl4is 504 mm Hg at this temperature, what is the vapor pressure of the CCl4over

this solution?

1. 504 mm Hg 3. 494 mm Hg

2. 514 mm Hg 4. 10.1 mm Hg

14.12. What mass of ethylene glycol (HOC2H4OH, molar mass = 62.0 g/mol) must be added to 125 g of

water to raise the boiling point by 1.0 C? (Kbpfor water = +0.512 deg/molal)

1. 1.95 g 3. 15 g

2. 0.244 g 4. 31.0 g

14.13. You dissolve 29.3 g of NaCl (molar mass = 58.5 g/mol) in 500. grams water. What is the boiling

point of this solution? Kbpfor water = +0.512 deg/molal

1. 100.512 C 3. 101.536 C

2. 98.976 C 4. 101.024 C

14.14. Concentrated salt solutions have boiling points lower than those calculated using the equation

!Tbp= Kbp m. Which of the following is a possible explanation of this observation?

1. positive ions repel each other more at high concentration

2. ions of opposite charge will tend to stay paired instead of breaking up

3. the water molecules will have a greater attraction for each other

4. concentrated solutions have small particles of non-dissolved salt, thus lowering the molality

14.15. After a can of carbonated soft drink is removed from the refrigerator, opened and left to stand

awhile, which of the following best describes the changes that cause the soda to go flat" (i.e. lose its

CO2content)?

1. lowering the CO2(g) pressure over the solution and raising of temperature

2. lowering the CO2(g) pressure over the solution

3. lowering the temperature

4. change (increase) in salt content

14.16. Which of the following is an example of the importance of osmosis?

1. distilling alcohol 3. salting roads for de-icing

2. salting meats for preservation 4. the use of antifreeze in the cooling system of cars

14.17. Erythritol is a compound that occurs naturally in algae and fungi. It is about twice as sweet as

sucrose. A solution of 2.50 g of erythritol in 50.0 g of water freezes at -0.762 C. (The freezing point


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Chapter 14 3

depression constant for water = -1.86 degrees/molal.) What is the molar mass of the compound?

1. 26.9 g/mol 3. 122 g/mol

2. 35.5 g/mol 4. 224 g/mol

14.18. Which solution is expected to have the higher boiling point?

1. 0.10 molal NaCl 2. 0.15 molal sugar?

14.19 The enthalpy of solution of sodium hydroxide is strongly exothermic. As the temperature

increases, the solubility

1. increases 2. decreases

14.20 In which aqueous solution is the vapor pressure of water lower?

1. 0.30 molal NH4NO3 2. 0.15 molal Na2SO4? ________

14.21. Arrange the following aqueous solutions in order of increasing vapor pressure at 25 C:

(i) 0.35mC2H4(OH)2(ethylene glycol, nonvolatile solute)

(ii) 0.50 msugar

(iii) 0.20 mKBr

(iv) 0.20 mNa2SO4

1. C2H4(OH)2 < sugar < KBr < Na2SO4

2. Na2SO4 < sugar < KBr < C2H4(OH)2

3. sugar < C2H4(OH)2 < KBr < Na2SO4

4. KBr < sugar < Na2SO4< C2H4(OH)2

14.22. Consider the following aqueous solutions:

1. 0.20 methylene glycol (a nonelectrolyte) 3. 0.10 mCaCl22. 0.12 mNaI 4. 0.12 mNa2SO4.

Which solution has the highest boiling point?


1. 0.20 methylene glycol (a nonelectrolyte) 3. 0.10 mCaCl2

2. 0.12 mNaI 4. 0.12 mNa2SO4.

Which solution has the highest freezing point?


1. 0.20 methylene glycol (a nonelectrolyte) 3. 0.10 mCaCl2

2. 0.12 mNaI 4. 0.12 mNa2SO4.

Which solution has the highest vapor pressure of water?

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