1

Outline Chapter 11 Crystals,

Ions, and Solutions

11-7. Evidence for Dissociation

11-8. Water

11-9. Water Pollution11-10. Acids11-11. Strong and Weak Acids 11-

12. Bases11-13. The pH Scale11-14. Salts

11-1. Ionic and Covalent Crystals11-2. The Metallic Bond11-3. Molecular Crystals11-4. Solubility11-5. Polar and Nonpolar Liquids11-6. Ions in Solution

2

11-1. Ionic and Covalent

Crystals

Most solids are crystalline, meaning the particles that compose them are arranged in repeated patterns. Amorphous solids have particles irregularly arranged. Crystalline solids fall into four classes:

1. Ionic

2. Covalent

3. Metallic

4. Molecular

Amorphous Glass

3

Table 11.1

4

11-1. Ionic and Covalent

Crystals

Ionic crystals are formed by the attraction between positive and negative ions.

1. Face-centered cubic ionic crystals have ions located at the corners and centers of the faces of a series of cubes.

2. Body-centered cubic ionic crystals have each ion located at the center of a cube at whose corners are ions of the other kind.

5

11-1. Ionic and Covalent

CrystalsCovalent crystals are formed when pairs of electrons are shared between adjacent atoms. Some crystals are neither wholly ionic nor wholly covalent but contain bonds of mixed character.

6

Dr. Tacy Hall’s Artificial Diamond Presses

Pictures to the left and below are of diamonds made

from graphite. Dr. Hall made

diamonds from peanut butter as

well.

7

11-2. The Metallic Bond

The metallic bond is formed by a "gas" of electrons that moves freely through the assembly of metal ions that form a solid metal. The metallic bond accounts for the characteristics of metals.

M M M M M M M M

M M M M M M M M

M M M M M M M M

M M M M M M M M

M M M M M M M M

e-

e-

e-

e-

e-

8

Fig. 11.10

The Electron Sea is responsible for the shiny

surfaces of metals.

9

11-3. Molecular Crystals

Some liquids and solids are formed through the action of van der Waals forces, named after the

Dutch physicist Johannes van der Waals.

Polar-polar interaction occurs between polar molecules whose positively and negatively charged ends cause them to

line up with the ends that have opposite charges adjacent.

10

Fig. 11.11

The water molecules in a snowflake are held together by van der Waals bonds. Ice is less

dense than its liquid and thus floats.

11

Fig. 11.15

Cling film owes its

properties to polar

molecules on its

surface.

12

11-3. Molecular Crystals

Non-polar-non-polar interaction occurs between non-polar molecules when the molecule's electrons at any given moment are distributed unevenly. This creates temporarily charged molecules whose

adjacent ends having opposite signs results in an attractive force.

13

11-3. Molecular Crystals

Examples of these weak temperary interactions is nitrogen gas. Nitrogen gas is normally non-polar but if the temperature is low enough, these non-polar molecules can form a liquid, liquid nitrogen.

14

11-4. Solubility

In a solution, the substance present in larger amount is the solvent; the other is the solute. The concentration of a solution is the amount of solute in a given amount of solvent. The solubility of a

substance is the maximum amount that can be dissolved in a given quantity of a particular solvent at a given temperature. Examples of solutions:

liquid in liquid- alcoholic drinkssolid in liquid- salt water

gas in liquid- sodas

gas in gas- airsolid in solid- metal alloy

15

11-4. Solubility

A saturated solution contains the maximum amount of solute possible at a given temperature; a supersaturated solution contains more dissolved solute than is normally possible at a given

temperature and is usually unstable.

16

Supersaturated and Supercooled

http://axiomsun.com/home/video/supercooled_water.html

http://www.youtube.com/watch?v=HnSg2cl09PI

17

11-4. Solubility

The solubilities of solids increase with increasing temperatures, while the solubilities of gases in liquids decrease with increasing temperatures. The boiling point of a solution is usually higher than that of

the pure solvent, and its freezing point is lower.

18

11-4. Solubility

19

11-5. Polar Liquids

A polar liquid is a substance whose molecules behave as if negatively charged at one end and

positively charged at the other. The molecules of a nonpolar liquid have uniform charge distributions.

20

11-5. Polar Liquids

Polar liquids dissolve only ionic and polar covalent compounds. Nonpolar liquids

dissolve only nonpolar covalent compounds.

21

Intermolecular Forces

Oδ-

Hδ+ Hδ+

Oδ-

Hδ+ Hδ+

Oδ-

Hδ+ Hδ+

Dipole-Dipole Forces

Solid

Liquid Gas

+ +

-

22

11-5. Polar Liquids

Soaps and Detergents have polar head and a non-polar tail. The

tail is attracted to the non-polar greasy dirt and the polar head is attracted to the

polar water molecules.

23

11-5. Polar Liquids

Dissociation refers to the separation of a compound into

ions when it dissolves.

24

11-5. Polar Liquids

Electrolytes are substances that dissociate into ions when dissolved in

water; nonelectrolytes are soluble covalent compounds that do not dissociate in

solution. Electrolytes in solution are able to conduct electric current.

25

11-6. Ions in Solution

Ions in solution have their own sets of properties that differ from their original

atoms and from the original solute. Dissociation is a type of chemical change. The properties of a solution

of an electrolyte are the sum of the properties of the ions present in the solution.

26

11-7. Evidence of Dissociation

In 1887, the Swedish chemist Svante Arrhenius proposed that many substances exist as ions in solution. His hypothesis was based

on two points:

1. Reactions between electrolytes

in solution occur almost instantaneously, but very slowly or not at all if the electrolytes are dry.

2. Electrolyte solutions have lower freezing points than comparable solutions of nonelectrolytes.

Svante Arrhenius

(1859-1927)

27

Fig. 11.31

This device used the color

difference between

chromic and dichromate

ions to measure the

alcohol concentration in a person’s

breath.

28

11-8. Water

Seawater has an average salt content, or salinity, of 3.5 percent.. "Hard" water is freshwater that contains Ca2+ and Mg2+ ions in solution; "soft" water is free of Ca2+ and Mg2+ ions.

These household water softeners are

ion-exchange resins.

Hard water left a deposit of scale in this

pipe.

29

11-8. Water

30

11-9. Water Pollution

Sources of water pollution include:

1. Industrial pollutants

2. Agricultural fertilizers and pesticides

3. Thermal pollution

The biochemical oxygen demand, or BOD, is the amount of oxygen needed to completely oxidize the organic material in a sample of water.

31

11-9. Water PollutionA municipal waste water treatment plant.

32

Fig. 11.37

Water pollution from a steel mill. Public anger has forced governments

to act against such abuse of the environment.

Below fertilizers caused algae raft.

33

11-10. Acids

An acid is a hydrogen-containing substance that increases the number of H+ ions present when the substance is dissolved in water. The H+ ions released when an acid dissociates in water combine with water

molecules to produce hydronium ions, H3O+.

The water solutions of acids taste sour, and acids change the color of litmus dye from blue to

red.

34

11-11. Strong Acids and Weak

Acids

Strong acids dissociate completely; weak acids dissociate only slightly. Some substances, such as carbon dioxide, do not contain hydrogen but produce acidic

solutions by reacting with water to liberate H+

ions from water molecules.

35

11-12. Bases

A base is a substance that contains hydroxide groups and whose solution in water increases the number of OH- ions present. Strong bases dissociate completely; weak bases dissociate

only slightly. The water solutions of bases have a bitter taste, a soapy feel, and turn red litmus to blue.The name alkali is sometimes used for a substance that dissolves in water to give a basic solution. The terms alkaline and basic

mean the same.

36

11-13. The pH Scale

The pH scale expresses the exact degree of acidity or basicity of a solution in terms of its H+ ion concentration. A solution that is neither acidic nor basic is

said to be neutral and has a pH of 7. Acidic solutions have pH values of less than 7. Basic solutions have pH values of more than 7.

37

Finding the [H+] from the pH.

To find the [H+] from the pH just insert the pH into 10-pH.

For example, if the pH is 4 the [H+] is 10-4.

If the pH is 6 the [H+] is 10-6

If the pH is 10 the [H+] is 10-10

If the pH is 8 the [H+] is

To find the pH from the [H+] just insert the [H+] into -log [H+].

For example, if the [H+] is 10-4 the pH is

If the [H+] is 10-9 the pH is

If the [H+] is 10-2 the pH is

9

2

10-8

4

38

pH = - log [H+]

[H+] = antilog (-pH) = 10-pH

If [H+] = 2.0 x 10-9 then

pH = -log(2.0 x 10-9) = 8.69897

pH =8.70 [H+] = 10-8.7

If pH = 3.2 then

[H+] = antilog(-3.2) = 6.31 x 10-4

Calculating pH and [H+]

pH Meter

39

Fill in the Blanks

pH [H+]

2.5 ______

8.2 ______

_____ 2.8x10-6

_____ 2.6x10-3

0.0032

6.3x10-9

5.6

2.6

40

11-14. Salts

When a basic solution is mixed with an acidic solution, the base destroys, or neutralizes, the properties of the acid and vice versa. The process is called neutralization. In neutralization reactions,

H+ and OH- ions join to form water molecules. Ions left in solution as a result of neutralization can combine to form a salt when the solution is evaporated to dryness. Most salts are crystalline solids that consist of positive metal ions and

negative nonmetal ions.

41

Lecture Quiz 11

1. What are the 4 types of crystalline solids? What type is diamond?

2. What is an electrolyte?

3. What happens when you cool a saturated solution?

4. What ions are primarily responsible for hard water?

5. What is the pH of a solution containing 3.7 x 10-5 M HCl?

42

43

Lecture Quiz 11

1. What are the 4 types of crystalline solids? Ionic, Covalent, Metallic, Molecular What type is diamond? Covalent

2. What is an electrolyte? Produces ions.

3. What happens when you cool a saturated solution?Solid forms on bottom.

4. What ions are primarily responsible for hard water? Ca2+and/or Mg2+

5. What is the pH of a solution containing 3.7 x 10-5 M HCl? 4.4

44

Lecture Quiz 11

1. Is water polar or non-polar?

2. What are 3 types of solutions?

3. What is meant by saturation?

4. What ions are primarily responsible for hard water?

5. What is BOD?

6. What is the pH of water?

45

Lecture Quiz 11

1. Is water polar or non-polar?

2. What are 3 types of solutions?Solid in liquid, gas in liquid, liquid in liquid, gas in gas, solid in solid, etc.

3. What is meant by saturation?You cannot dissolve anymore solute in the solvent.

4. What ions are primarily responsible for hard water? Ca2+ and Mg2+

5. What is BOD? Biological Oxygen Demand

6. What is the pH of water? 7