11: Intermolecular Forces and Liquids

Prelude

Exercise \(\PageIndex{1a}\)

What are the four common types of bonds?

Answer

Ionic, Polar covalent, covalent and metallic

 

Exercise \(\PageIndex{1b}\)

Do metals have high or low electronegativities?

Answer

low.

 

Exercise \(\PageIndex{1c}\)

Do nonmetals have high or low electronegativities?

Answer

high.

 

Exercise \(\PageIndex{1d}\)

Which element has the highest electronegativy

Answer

Fluorine.

 

 

States of Matter

Exercise \(\PageIndex{2a}\)

What are the three common exothermic transitions

Answer

Freezing, Condensation and deposition.

 

Exercise \(\PageIndex{b}\)

What are the three common endothermic transitions

Answer

sublimation, boiling and melting

 

Exercise \(\PageIndex{2c}\)

When a substance freezes does it gain or lose heat?

Answer

It loses heat

 

 

Ion-Dipole Forces

 

Exercise \(\PageIndex{3a}\)

For each pair, predict which would have the greater ion-dipole interaction with water.

1. Lithium or potassium cations
2. Lithium or Boron cations
3. fluoride or chloride
4. sulfide or chloride

Answer a

Lithium as they have the same charge and it is smallest

Answer b

Boron as it is both smaller and has a higher charge

Answer c

fluoride as they have the same charge and it is smaller

Answer d

sulfide as although it is larger, it has a greater charge

 

Dipole-Dipole Forces

 

Exercise \(\PageIndex{4a}\)

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

Answer

AsH₃

 

Dispersive Forces

 

Exercise \(\PageIndex{5a}\)

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

Answer

d. Te

 

Exercise \(\PageIndex{5b}\)

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

Answer

I₂

 

Hydrogen Bonding

 

Exercise \(\PageIndex{6a}\)

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 \(\PageIndex{6b}\)

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 \(\PageIndex{6c}\)

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

Answer

NH₄⁺

 

Exercise \(\PageIndex{6d}\)

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

Answer

109°

 

Properties of Liquids

 

Exercise \(\PageIndex{7a}\)

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 \(\PageIndex{7b}\)

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 \(\PageIndex{7c}\)

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

Answer

a. He, it is the lightest and least polarizable (so it has weakest intermolecular forces) and thus the easiest to boil

 

Exercise \(\PageIndex{7d}\)

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

Answer

H₂S < H₂Se < H₂Te < H₂O

 

Exercise \(\PageIndex{7e}\)

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

Answer

CH₄ < NH₃ < HF < H₂O

 

Exercise \(\PageIndex{7f}\)

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

Answer

SnH₄

 

Exercise \(\PageIndex{7g}\)

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

Answer

CH₄

 

Exercise \(\PageIndex{7h}\)

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

Answer

NH₃

 

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

Exercise \(\PageIndex{7i}\)

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 \(\PageIndex{7j}\)

If one of the compounds in the above question 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 \(\PageIndex{7k}\)

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 \(\PageIndex{7L}\)

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

e

Exercise \(\PageIndex{7M}\)

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

e

Exercise \(\PageIndex{7n}\)

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. Incompressible, the shape of a portion, compressible, the volume and shape
5. Incompressible, the volume and shape, compressible, the shape

Answer

d. Incompressible, the shape of a portion, compressible, the volume and shape

 

Exercise \(\PageIndex{7o}\)

Choose the molecule that has the highest boiling point.

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

Answer

e. C₂I₆

 

Exercise \(\PageIndex{7p}\)

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

Answer

Br₂

 

Exercise \(\PageIndex{7q}\)

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 \(\PageIndex{7r}\)

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 \(\PageIndex{7s}\)

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 \(\PageIndex{7t}\)

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 it is much heavier, even though CHF₃ is polar.  It  also has strong London dispersion forces

Answer d

CH₃OH due to hydrogen bonding

 

Exercise \(\PageIndex{7u}\)

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 it being more polarizable and having a heavier mass

 

Exercise \(\PageIndex{7v}\)

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 heavier mass

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 \(\PageIndex{7w}\)

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 there being less kinetic energy

 

Exercise \(\PageIndex{7x}\)

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

Answer

C₆H₆ < C₆H₅SH < C₆H₅OH

 

Exercise \(\PageIndex{7y}\)

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 is much heavier, and it has very high dispersion forces, even though chlorform has a permenant dipole

 

General Questions

Exercise \(\PageIndex{8a}\)

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 \(\PageIndex{8b}\)

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 \(\PageIndex{8c}\)

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 \(\PageIndex{8d}\)

Which force is strongest?

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

Answer

d. covalent

 

Exercise \(\PageIndex{8e}\)

Place 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 \(\PageIndex{8f}\)

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 \(\PageIndex{8g}\)

What is the predominant 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 \(\PageIndex{8h}\)

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

Answer

They are all symetric homonuclear diatomics with London dispersion forces.  Iodine is the heaviest and most polarizable, and so has the highest boiling point.  Flourine is the lightest and least polarizable, so it has the lowest boiling point (it is easier to boil), and Bromine is in the middle.

 

Exercise \(\PageIndex{8i}\)

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 \(\PageIndex{8j}\)

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 \(\PageIndex{8k}\)

The molecules in liquid 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