Brown - Chemistry: The Central Science 14th Edition - Chapter 11

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Ch.11 - Liquids and Intermolecular Forces

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Brown 14th Edition

Ch.11 - Liquids and Intermolecular Forces

Problem 15a
(a) Which type of intermolecular attractive force operates between all molecules?
Problem 15b
(b) Which type of intermolecular attractive force operates only between polar molecules?
Problem 15c
(c) Which type of intermolecular attractive force operates only between the hydrogen atom of a polar bond and a nearby small electronegative atom?
Problem 16
Which is generally stronger, intermolecular interactions or intramolecular interactions?
Problem 16b
(b) Which of these kinds of interactions are broken when a liquid is converted to a gas?
Problem 17
Describe the intermolecular forces that must be overcome to convert these substances from a liquid to a gas: (a) SO₂, (b) CH₃COOH, (c) H₂S.
Problem 18a,d
Which type of intermolecular force accounts for each of these differences? (a) CH₃OH boils at 65 °C; CH₃SH boils at 6 °C. (d) Acetone boils at 56 °C, whereas 2-methylpropane boils at -12 °C.
Problem 18b,c
Which type of intermolecular force accounts for each of these differences? (b) Xe is a liquid at atmospheric pressure and 120 K, whereas Ar is a gas under the same conditions. (c) Kr, atomic weight 84 amu, boils at 120.9 K, whereas Cl₂, molecular weight about 71 amu, boils at 238 K.
Problem 19
(a) List the following molecules in order of increasing polar- izability: GeCl4, CH4, SiCl4, SiH4, and GeBr4. (b) Predict the order of boiling points of the substances in part (a).
Problem 20b
True or false: (b) For the noble gases the dispersion forces decrease while the boiling points increase as you go down the column in the periodic table.
Problem 20e
True or false: (e) The larger the atom, the more polarizable it is.
Problem 21a
Which member in each pair has the greater dispersion forces? (a) H₂O or H₂S,
Problem 21b,c
Which member in each pair has the greater dispersion forces? (b) CO₂ or CO, (c) SiH₄ or GeH₄.
Problem 22
Which member in each pair has the stronger intermolecular dispersion forces? (a) Br₂ or O₂ (b) CH₃CH₂CH₂CH₂SH or CH₃CH₂CH₂CH₂CH₂SH (c) CH₃CH₂CH₂Cl or (CH₃)₂CHCl
Problem 25
(a) What atoms must a molecule contain to participate in hydrogen bonding with other molecules of the same kind? (b) Which of the following molecules can form hydrogen bonds with other molecules of the same kind: CH₃F, CH₃NH₂, CH₃OH, CH₃Br?
Problem 26
Rationalize the difference in boiling points in each pair: (a) HF (20 °C) and HCl (-85 °C) (b) CHCl3 (61 °C) and CHBr3 (150 °C) (c) Br2 (59 °C) and ICl (97 °C)
Problem 27a
Ethylene glycol (HOCH2CH2OH), the major substance in antifreeze, has a normal boiling point of 198 °C. By comparison, ethyl alcohol (CH3CH2OH) boils at 78 °C at atmospheric pressure. Ethylene glycol dimethyl ether (CH3OCH2CH2OCH3) has a normal boiling point of 83 °C, and ethyl methyl ether (CH3CH2OCH3) has a nomral boiling point of 11 °C. (a) Explain why replacement of a hydrogen on the oxygen by a CH3 group generally results in a lower boiling point.
Problem 27b
Ethylene glycol (HOCH₂CH₂OH), the major substance in antifreeze, has a normal boiling point of 198 °C. By comparison, ethyl alcohol (CH₃CH₂OH) boils at 78 °C at atmospheric pressure. Ethylene glycol dimethyl ether (CH₃OCH₂CH₂OCH₃) has a normal boiling point of 83 °C, and ethyl methyl ether (CH3CH2OCH3) has a nomral boiling point of 11 °C. (b) What are the major factors responsible for the difference in boiling points of the two ethers?
Problem 28
Based on the type or types of intermolecular forces, predict the substance in each pair that has the higher boiling point: (a) propane (C₃H₈) or n-butane (C₄H₁₀) (b) diethyl ether (CH₃CH₂OCH₂CH₃) or 1-butanol (CH₃CH₂CH₂CH₂OH) (c) sulfur dioxide (SO₂) or sulfur trioxide (SO₃) (d) phosgene (Cl₂CO) or formaldehyde (H₂CO)
Problem 29
Look up and compare the normal boiling points and normal melting points of H2O and H2S. Based on these physical properties, which substance has stronger intermolecular forces? What kinds of intermolecular forces exist for each molecule?
Problem 31
A number of salts containing the tetrahedral polyatomic anion, BF₄^-, are ionic liquids, whereas salts containing the somewhat larger tetrahedral ion SO₄^2-do not form ionic liquids. Explain this observation.
Problem 32
The generic structural formula for a 1-alkyl-3-methylimid- azolium cation is where R is a -CH2(CH2)nCH3 alkyl group. The melting points of the salts that form between 1-alkyl-3-methylimidazolium cation and the PF6- anion are as follows: R = CH2CH3 (m.p. = 60 °C), R = CH2CH2CH3 (m.p. = 40 °C), r = CH2CH2CH2CH3 (m.p. = 10 °C), and R = CH2CH2CH2CH2CH2CH3 (m.p. = -61 °C). Why does the melting point decrease as the length of alkyl group increases?
Problem 33b
(b) What is the relationship between viscosity and temperature?
Problem 33c
(c) Why do substances with high surface tension also tend to have high viscosities?
Problem 34a,c
Based on their composition and structure, list CH₂Cl₂, CH₃CH₂CH₃, and CH₃CH₂OH in order of (a) increasing intermolecular forces (c) increasing surface tension
Problem 35b
Liquids can interact with flat surfaces just as they can with capillary tubes; the cohesive forces within the liquid can be stronger or weaker than the adhesive forces between liquid and surface:
(b) Which of these diagrams, i or ii, rep- resents what happens when water is on a nonpolar surface?
Problem 36
Hydrazine (H2NNH2), hydrogen peroxide (HOOH), and water (H2O) all have exceptionally high surface tensions compared with other substances of comparable molecular weights. What structural property do these substances have in common, and how might that account for the high surface tensions?
Problem 37
The boiling points, surface tensions, and viscosities of water and several alcohols are as shown below: (b) How do you explain the fact that propanol and ethylene glycol have similar molecular weights (60 versus 62 amu), yet the viscosity of ethylene glycol is more than 10 times larger than propa- nol?
Problem 39
Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (a) When ice is heated, it turns to water. (b) Wet clothes dry on a warm summer day. (c) Frost appears on a window on a cold winter day. (d) Droplets of water appear on a cold glass of lemonade.
Problem 40c
Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (c) Rubbing alcohol in an open container slowly disappears.