11: Intermolecular Forces and Liquids

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General Questions

Exercise \(\PageIndex{1}\)

What is the dominant intermolecular force in H₂?

1. London Dispersion (instantaneous dipole-induced dipole)
2. dipole-dipole
3. ion-dipole
4. hydrogen bonding

Answer

a. London Dispersion (instantaneous dipole-induced dipole)

Exercise \(\PageIndex{2}\)

What is the major intermolecular force in H₂O? 

1. London Dispersion (induced dipole-induced dipole)
2. dipole-dipole
3. ion-dipole
4. hydrogen bonding

Answer

d. hydrogen bonding

Exercise \(\PageIndex{3}\)

What is the major intermolecular force responsible for the dissolution of NaCl in H₂O?

1. London Dispersion (induced dipole-induced dipole)
2. dipole-dipole
3. ion-dipole
4. hydrogen bonding

Answer

c. ion-dipole

Exercise \(\PageIndex{4}\)

Which force is strongest?

1. dipole/dipole
2. ion/dipole
3. London Dispersion
4. covalent

Answer

d. covalent

Exercise \(\PageIndex{5}\)

Hydrogen bonding is a special case of:

1. dipole-dipole forces
2. ion-dipole forces
3. covalent bonding
4. London Dispersion Forces

Answer

a. dipole-dipole force

Exercise \(\PageIndex{6}\)

Which has the highest boiling point? (F₂, Cl₂, Br₂, I₂)

Answer

d. I₂, these are all homonuclear diatomics, and Iodine is both the heaviest (largest mass) and most polarizable (largest volume).

Exercise \(\PageIndex{7}\)

Which has the highest boiling point? (HF, HCl, HI, HBr)

Answer

a. HF, although it is the lightest (which would have you think it would have a low boiling point), it has strong hydrogen bonds, which take a lot of energy to overcome, and so has a high boiling point.

Exercise \(\PageIndex{8}\)

Which of the following molecules are not involved with hydrogen bonding?

1. H₂,NH₃
2. HI,HBr
3. HF,NH₃
4. HCOOH,H₂O

Answer

b. HI, HBr

Exercise \(\PageIndex{9}\)

Which has the lowest boiling point? (He, Ne, Kr, Ar)

Answer

a. He

Exercise \(\PageIndex{10}\)

Which is more polarizable? (O, S, Se, Te)

Answer

d. Te

Exercise \(\PageIndex{11}\)

Placed the following compounds in the order of instantaneous dipole, dipole/dipole and hydrogen bonding as the primary intermolecular forces. (H₂O, H₂Se, CH₄)

Answer

CH₄, H₂Se, H₂O

Exercise \(\PageIndex{12}\)

Arrange the following compounds in order of increasing boiling points. (H₂O, H₂S, H₂Se, H₂Te)

Answer

H₂S < H₂Se < H₂Te < H₂O

Exercise \(\PageIndex{13}\)

Arrange the following compounds in order of increasing boiling point. (H₂O, HF, NH₃, CH₄)

Answer

CH₄ < NH₃ < HF < H₂O

Exercise \(\PageIndex{14}\)

Which compound is the most polarizable? (I₂, H₂, F₂, Br₂)

Answer

I₂

Exercise \(\PageIndex{15}\)

Which species cannot be involved with hydrogen bonding? (HF, H₂O, NH₃, NH₄⁺)

Answer

NH₄⁺

Exercise \(\PageIndex{16}\)

What intermolecular force is responsible for the dissolution of oxygen into water?

1. hydrogen bonding
2. instantaneous-induced dipole
3. dipole-induced dipole
4. dipole-dipole

Answer

C. dipole-induced dipole

Exercise \(\PageIndex{17}\)

Which has the highest boiling point? (CH₄, SiH₄, GeH₄, SnH₄)

Answer

SnH₄

Exercise \(\PageIndex{18}\)

Which has the lowest boiling point? (CH₄, SiH₄, GeH₄, SnH₄)

Answer

CH₄

Exercise \(\PageIndex{19}\)

Which has the highest boiling point? (NH₃, PH₃, CH₄, SiH₄)

Answer

NH₃

Exercise \(\PageIndex{20}\)

What angle best approximates the geometric structure of ice? (90°, 109°, 120°, 180°)

Answer

109°

11.1: Vapor pressure of four different compounds.  Use figure 11.1 to solve the following questions.

Exercise \(\PageIndex{21}\)

Which set of curves would represent the effect of increasing temperature on the vapor pressure of a liquid?

1. A & B
2. C & D
3. All of them
4. None of them

Answer

a. A & B

Exercise \(\PageIndex{22}\)

The normal boiling point is defined as: 

1. 100°C

2. The boiling pt. at 1 atm

3. The boiling pt. on planet earth

4. None of the above

Answer

b. The boiling pt. at 1 atm

Exercise \(\PageIndex{23}\)

The normal boiling point of diethyl ether is 34.6°C and of water is 100°C. Which has the higher vapor pressure at 20°C?

1. water
2. diethyl ether
3. they are the same
4. it depends on your elevation

Answer

b. diethyl ether

Exercise \(\PageIndex{24}\)

If one of the compounds in question 1 is diethyl ether and the other is water, curve___is diethyl ether and curve___is water.

1. A,B
2. B,A
3. C,D
4. D,C

Answer

a. A,B

Exercise \(\PageIndex{25}\)

A liquid is _____  and assumes _____ of its container whereas a gas is _____ and assumes _____ of its container.

1. Compressible, the volume and shape, condensed, the shape
2. Compressible, the volume, compressible, the volume and shape
3. Condensed, the volume and shape, condensed, the volume and shape
4. Not compressible, the shape of a portion, compressible, the volume and shape
5. Not compressible, the volume and shape, compressible, the shape

Answer

d. Not compressible, the shape of a portion, compressible, the volume and shape

Exercise \(\PageIndex{26}\)

Choose the following molecule that exhibits dipole-dipole attractions? (AsH₃, BCl₃, Cl₂, CO₂, XeF₄)

Answer

AsH₃

Exercise \(\PageIndex{27}\)

What is the predominant intermolecular force in KBr?

1. Dipole-dipole attraction
2. Hydrogen-bonding
3. Ion-dipole attraction
4. Ionic bonding
5. London-dispersion forces

Answer

d. Ionic bonding

Exercise \(\PageIndex{28}\)

What are the principal difference in the normal boiling points of ICl (97°C; molecular mass 162 amu) and Br₂ (59°C; molecular mass 160 amu)?

1. Both dipole-dipole interactions and London-dispersion forces
2. Both hydrogen-bonding and dipole-dipole interactions
3. Dipole-dipole interactions
4. Hydrogen bonding
5. London-dispersion forces

Answer

c. Dipole-dipole interactions

Exercise \(\PageIndex{29}\)

Explain the reason why iodine is a solid, bromine is a liquid, and chlorine is a gas at room temperature.

Answer

Van der Waals forces increase going down the periodic table. Thus Chlorine has the weakest van der Waals forces and Iodine has the strongest with bromine being in the middle.

Exercise \(\PageIndex{30}\)

The _____ is the attractive force between an instantaneous dipole and an induced dipole.

1. Dipole-dipole attraction
2. Hydrogen-bonding
3. Ion-dipole attraction
4. Ionic bonding
5. London dispersion forces

Answer

e. London dispersion forces

Exercise \(\PageIndex{31}\)

Choose the ethane molecule that has the highest boiling point.

1. C₂Br₆
2. C₂Cl₆
3. C₂F₆
4. C₂H₆
5. C₂I₆

Answer

e. C₂I₆

Exercise \(\PageIndex{1=32}\)

What is the major attractive force that exists among different I₂ (elemental iodine, I₂, is a solid at room temperature) molecules in the solid?

1. Covalent-ionic interactions
2. Dipole-dipole attractions
3. Dipole-dipole rejections
4. Ionic-dipole interactions
5. London dispersion forces

Answer

e. London dispersion forces

Exercise \(\PageIndex{33}\)

Hydrogen bonding is a special case of what other intermolecular forces?

1. Dipole-dipole attractions
2. Ion-dipole attraction
3. Ion-ion interactions
4. London-dispersion forces
5. None of these

Answer

a. Dipole-dipole attractions

Exercise \(\PageIndex{34}\)

Which of the following has the highest boiling point? (N₂, Br₂, H₂, Cl₂, O₂)

Answer

Br₂

Exercise \(\PageIndex{35}\)

The molecules in C₁₂H₂₆ are held together by _____.

1. Dipole-dipole interactions
2. Dispersion forces
3. Hydrogen bonding
4. Ion-dipole interactions
5. Ion-ion interactions

Answer

b. Dispersion forces

Exercise \(\PageIndex{36}\)

The shape of a liquid’s meniscus is determined by _____.

1. the relative magnitudes of cohesive forces in the liquid and adhesive forces between the liquid and its container
2. the type of material the container is made of
3. the viscosity of the liquid
4. the volume of the liquid

Answer

a. the relative magnitudes of cohesive forces in the liquid and adhesive forces between the liquid and its container

Exercise \(\PageIndex{37}\)

Viscosity is _____.

1. Inversely proportional to molar mass
2. The “skin” on a liquid surface caused by intermolecular attraction
3. The resistance to flow
4. The same as density
5. Unaffected by temperature

Answer

c. The resistance to flow

Exercise \(\PageIndex{38}\)

What property is responsible for the “beading up” of water?

1. density
2. hydrogen bonding
3. surface tension
4. vapor pressure
5. viscosity

Answer

c. surface tension

Exercise \(\PageIndex{39}\)

Explain which substance in each of the following pairs is likely to have the higher normal melting point: (a) HCl or NaCl; (b) C₂H₅OC₂H₅ (diethyl ether) or C₄H₉OH (butanol); (c) CHI₃ or CHF₃; (d) C₂H₄ or CH₃OH

Answer a

NaCl, because it is an ionic compound not molecular

Answer b

butanol due to hydrogen bonding in butanol not in diethyl ether

Answer c

CHI₃ because of stronger London dispersion forces

Answer d

CH₃OH due to hydrogen bonding

Exercise \(\PageIndex{40}\)

Explain which substance in each of the following pairs is likely to have the higher normal melting point: (a) H₂S or H₂O; (b) NH₃ or PH₃; (c) KBr or CH₃Br; (d) CH₄ or SiH₄.

Answer a

H₂O because hydrogen bonding is stronger than dipole-dipole bonds

Answer b

NH₃ because hydrogen bonding can occur with 2 of the molecules

Answer c

KBr due to being an ionic compound not molecular

Answer d

SiH₄ due to stronger intermolecular forces and electrons

Exercise \(\PageIndex{41}\)

Predict the shapes of each of the following molecules and identify the member of each pair with the higher boiling point using VESPR models: (a) PBr₃ or PF₃; (b) SO₂ or CO₂; (c) BF₃ or BCl₃.

Answer a

PBr₃ due to stronger dipole-dipole bonds

Answer b

 SO₂ due to dipole-dipole bonds being stronger than London dispersion forces

Answer c

BCl₃ has stronger van der Waal's forces

Exercise \(\PageIndex{42}\)

Determine which liquid in each of the following pairs has the greater surface tension: (a) cis-dichloroethene or trans-dichloroethene; (b) benzene at 20°C or benzene at 60°C.

Answer a

cis-dichloroethene due to the molecule being polar and having both dipole-dipole and van der Waals forces

Answer b

benzene at 20°C due to stronger intermolecular forces at a cooler temperature

Exercise \(\PageIndex{43}\)

Rank the following molecules in order of increasing viscosity at 50°C: C₆H₅SH, C₆H₅OH, C₆H₆.

Answer

C₆H₆ < C₆H₅SH < C₆H₅OH

Exercise \(\PageIndex{44}\)

The boiling point of chloroform (CHCl₃) is lower than that of carbon tetrachloride (CCl₄). Since chloroform is polar and carbon tetrachloride is not, with consideration of the dipole-dipole forces would predict that chloroform would have the higher boiling point. How can we account for the observed order of the boiling points?

Answer

Carbon tetrachloride has a higher boiling point because the dispersion forces are extensive enough to be stronger than the dipole-permanent dipole interactions in chloroform.