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Section 13.1 Uniquely Water

Section 13.2 Solutions and Their Properties

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Section 13.1

Uniquely Water

• Describe the uniqueness of water as a chemical substance.

• Model the three-dimensional geometry of a water molecule.

• Relate the physical properties of water to its molecular structure.

Section 13.1

Uniquely Water

interparticle forces: the forces between the particles that make up a substance

Section 13.1

Uniquely Water

hydrogen bondingsurface tensioncapillarityspecific heat

The molecular shape of water gives it its unusual properties.

Section 13.1

Physical Properties of Water• Water behaves differently from other

substances.

Section 13.1

Physical Properties of Water (cont.)

• Water is the only substance on Earth that exists in large quantities in all three common states of matter.

• Unlike most substances, water is less dense as a solid.

Section 13.1

Physical Properties of Water (cont.)

• There is a large electronegativity difference between the covalently bonded hydrogen and oxygen.

Section 13.1

Interparticle Forces in Water• Attractive forces between objects do not create

interactions between just two objects.

• Water molecules have such strong electrical forces that they will orient themselves like magnets, with the opposite poles of different magnets pulled toward one another.

Section 13.1

Interparticle Forces in Water (cont.)

• The hydrogen bonds between water molecules are stronger than typical dipole-dipole attractions because the bond between hydrogen and oxygen is highly polar.

Section 13.1

Interparticle Forces in Water (cont.)

• The formation of a connection between the hydrogen atoms on one molecule and a highly electronegative atom on another is called hydrogen bonding.

Section 13.1

Interparticle Forces in Water (cont.)

• Any molecule that has O–H bonds has the potential to form hydrogen bonds.

Section 13.1

• Many of the unique properties of water are due to the hydrogen bonding that occurs between water molecules.

States of Water

Section 13.1

States of Water (cont.)

Section 13.1

• The interparticle hydrogen bonds hold the water molecules together so strongly that it is difficult for them to escape into a gaseous state, which is why water has such a high boiling point.

States of Water (cont.)

Section 13.1

• The density of water changes as its temperature changes.

• As water cools from 60°C, its volume decreases and its density increases.

States of Water (cont.)

Section 13.1

• Water reaches its minimum volume and its maximum density at about 4°C.

States of Water (cont.)

Section 13.1

• A water molecule forms a drop because of surface tension, which is the force needed to overcome interparticle attractions and break through the surface of a liquid or spread the liquid out.

More Evidence for Water’s Interparticle Forces

Section 13.1

• The higher the surface tension, the more resistant the liquid is to having its surface broken.

– liquid mercury becoming round beads when placed on a smooth surface

More Evidence for Water’s Interparticle Forces (cont.)

Section 13.1

• Capillarity results from interparticle attractive forces between the molecules of liquid and the attractive forces between the liquid and the tube that contains it.

– the rising of liquids in narrow tubes

More Evidence for Water’s Interparticle Forces (cont.)

Section 13.1

• If the water in the cylinder has too much mass, the liquid surface forms a concave meniscus shape.

More Evidence for Water’s Interparticle Forces (cont.)

Section 13.1

• Specific heat measures the amount of heat, in joules, needed to raise the temperature of 1 g of substance by 1°C.

More Evidence for Water’s Interparticle Forces (cont.)

Section 13.1

More Evidence for Water’s Interparticle Forces (cont.)

Section 13.1

• Water has the highest specific heat because it must absorb or release more heat for its temperature to change by one Celsius degree.

More Evidence for Water’s Interparticle Forces (cont.)

Section 13.1

• Water serves as a great heat reservoir that moderates the temperature at Earth’s surface.

More Evidence for Water’s Interparticle Forces (cont.)

– extreme temperatures in the desert

Section 13.1

• Vaporization of a liquid is an endothermic (energy-absorbing) process.

• Condensation is an exothermic (energy-releasing) process.

• Water has a high heat of vaporization and loses a great deal of heat when it condenses.

More Evidence for Water’s Interparticle Forces (cont.)

Section 13.1

• Most of the water on Earth is not pure but present in solutions.

• Water is known as the universal solvent.

• The attraction of water molecules for other molecules, as well as for one another, accounts for water’s solvent properties.

Water: the universal solvent

Section 13.1

Section Assessment___ is the only substance on Earth that exists in large quantities in all three common states of matter.

A. Hydrogen

B. Oxygen

C. Iron

D. Water

Section 13.1

Section AssessmentWhat other biological molecules have the ability to form hydrogen bonds?

A. proteins

B. nucleic acids

C. carbohydrates

D. all of the above

End of Section 13.1

Section 13.2

Solutions and Their Properties

• Compare and contrast the ability of water to dissolve ionic and covalent compounds.

• Determine the concentrations of solutions.• Compare and contrast colligative properties

of solutions.

Section 13.2

Solutions and Their Properties

capillarity: the rising of a liquid in a narrow tube, sometimes called capillary action

Section 13.2

Solutions and Their Properties

dissociationunsaturated solutionsaturated solutionsupersaturated

solution

heat of solutionosmosiscolloidTyndall effect

Water dissolves a large number of ionic and covalent compounds.

Section 13.2

The Dissolving Process• The submicroscopic interactions of water

with solute particles determine the extent to which water is able to dissolve the solute.

• The process by which the charged particles in an ionic solid separate from one another is called dissociation.

• Ionic substances conduct electricity because there are free electrons in the solution.

• Free electrons allow conduction of electricity.

Section 13.2

The Dissolving Process (cont.)

Section 13.2

The Dissolving Process (cont.)

• When a covalent compound is dissolved in water, the covalent molecules are simply separated from one another and remain neutral.

Section 13.2

The Dissolving Process (cont.)

• Sugar dissolved in water is a nonconductor.

• No ions are present, so there are no free electrons to conduct an electric charge.

• Sugar stays in the molecular form.

Section 13.2

The Dissolving Process (cont.)

• Dissolving occurs when similarities exist between the solvent and the solute.

• “Like dissolves like”

• Ionic salts dissolve in water because both salts and water are polar.

• Oil and water are not similar and do not mix because oil is nonpolar and water is polar.

Section 13.2

• The concentration of a solution is the relative amount of solute and solvent.

Solution Concentrate

– A concentrated solution has more solute than solvent.

– Frozen concentrated orange juice has more orange because the water has been removed.

– A diluted solution has more solvent that solute.

– Water is added to concentrated orange juice to make it dilute.

Section 13.2

• If the amount of solute dissolved is less than the maximum that could be dissolved, the solution is an unsaturated solution.

• Solubility changes with temperature.

• At higher temperatures, usually, more solute will dissolve in solvent.

• If a crystal of solute is dropped into an unsaturated solution, the crystal will dissolve.

Solution Concentrate (cont.)

Section 13.2

• A solution that holds the maximum amount of solute per amount of the solution is called a saturated solution.

• Solubility changes with temperature.

• At higher temperatures, usually, more solute will dissolve in solvent.

• If a crystal of solute is dropped into a saturated solution, the crystal will fall to the bottom of the container and will not dissolve.

Solution Concentrate (cont.)

Section 13.2

• A supersaturated solution is an unstable solution containing more solute than the usual maximum.

• Supersaturated solutions are prepared by heating a substance until the solute is dissolved, then cooling slowly without disturbing the solution.

• If a crystal of solute is dropped into a supersaturated solution, the crystal will disturb the stability of the solution, and all the extra solute will fall out of solution at one time.

Solution Concentrate (cont.)

Section 13.2

• Temperature has a significant effect on solubility for most solvents.

• As you can see, most solutions increase solubility as temperature is increased.

• Which salt in the graph did not follow this pattern?

Solution Concentrate (cont.)

Section 13.2

• A solution always has a lower freezing point than the corresponding pure solvent.

• An ionic solute produces a lower freezing point than a covalent one because it dissociates into ions.

• This is called freezing point depression.

• Example: salt on icy roads.

Solution Properties and Applications

Section 13.2

• The boiling point of a solution is higher than the boiling point of the pure solvent.

• An ionic solute produces a higher boiling point than a covalent one because it dissociates into ions.

• This is called boiling point elevation.

• Example: adding salt to water to cook foods more quickly.

Solution Properties and Applications (cont.)

Section 13.2

Solution Properties and Applications (cont.)•The flow of solvent molecules through a selectively permeable membrane, driven by concentration difference, is called osmosis.

Section 13.2

• The solubility of gas in a liquid depends on the pressure of the gas pushing down on the liquid and the temperature.

Solutions of Gases in Water

Section 13.2

• The higher the pressure, the more soluble is the gas.

• As temperature increases, the solubility decreases.

• This is why soda kept cold keeps its “fizz” longer, and why warm soda becomes flat more quickly.

Solutions of Gases in Water (cont.)

Section 13.2

• Colloids are mixtures that contain particles that are evenly distributed through a dispersing medium and do not settle out over time.– The main difference between a colloid and

a solution is the size of the solute particles.

Solutions of Gases in Water (cont.)

• The Tyndall effect is the scattering effect caused when light passes through a colloid.

• Air is a colloid, so light will scatter in it.

• Think of a projector light in a theater, or headlights through fog.

Section 13.2

1. How might rubbing and scrubbing with soap help to remove a greasy stain from clothing?

• Rubbing and scrubbing break down the grease into smaller droplets. The surfactant (soap or detergent) is then able to surround each grease particle with a thin layer, separating it from the clothing and making it easier to wash away.

Everyday Chemistry (page 455)

Section 13.2

2. Some ancient people, such as the Egyptians and Romans, washed by rubbing themselves with oil, which was then scraped off. Compare the effectiveness of this method with the use of soap and water today.

•Washing with oil is almost as effective as washing with soap.

•Oil and dirt on the body would dissolve in the washing oil.

•The main difficulty would be in removing the wash oil completely from the skin.

Everyday Chemistry (page 455)

Section 13.2

Section AssessmentA ___ solution has more solvent that solute.

A. diluted

B. concentrated

C. versatile

D. diffused

Section 13.2

Section AssessmentWhich solution is the most unstable?

A. unsaturated

B. saturated

C. supersaturated

Study Guide 1

Key Concepts• The polarity of the water molecule is the source of

many of water’s unusual physical properties.

• Hydrogen bonds form between the hydrogen atoms of one molecule and a highly electronegative atom of another.

• Specific heat is the amount of heat needed to raise the temperature of 1 g of a substance by 1°C.

Study Guide 2

Key Concepts• Like dissolves like.

• Interparticle forces between solvent and solute strongly influence solution formation.

• Ionic compounds dissociate when they dissolve in water.

• Solutions can be unsaturated, saturated, or supersaturated.

Study Guide 2

Key Concepts

• Temperature affects solubility.

• Molarity is the number of moles of solute dissolved per liter of solution.

• Colligative properties of solutions, such as freezing-point depression and boiling-point elevation, are dependent only upon concentration of solute particles.

Chapter Assessment 1

Many of the unique properties of water are due to: A. the attractive forces between the nucleus

and electrons

B. the oxygen bonding between water molecules

C. its density

D. hydrogen bonding between water molecules

Chapter Assessment 2

What causes liquid mercury to form rounded beads on a smooth surface?

A. low electronegativity

B. the temperature of the surface

C. capillary action

D. surface tension

Chapter Assessment 3

The oceans of Earth are examples of what kind of solutions?

A. unsaturated

B. saturated

C. supersaturated

Chapter Assessment 4

For most solutes, the process of dissolving in a solvent is a(n) ___ process.

A. saturation

B. electronegative

C. endothermic

D. exothermic

Chapter Assessment 5

___ is the number of moles of solute per liter of solution.

A. Molarity

B. Heat of solution

C. Dissociation

D. Capillarity

STP 1

Water forms a concave meniscus and mercury produces a convex meniscus.

A. true

B. false

STP 2

Which substance has the highest specific heat?

A. ethanol

B. water

C. wood

D. gold

STP 3

Adding salt to water does what to the boiling point?

A. It raises the boiling point.

B. It lowers the boiling point.

C. It does not affect the boiling point.

STP 4

The main difference between a colloid and a solution is:

A. the size of the solute particles

B. the molarity of the solute

C. the saturation of the solute

D. the temperature of the solvent

STP 5

The freezing point of a solution is always ___ than the corresponding pure solvent.

A. lower

B. higher

C. the same as

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Table 13.1 The Uniqueness of Water

Figure 13.15 Dissolution of compounds

Figure 13.28 Osmosis

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