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CHEMISTRY & YOU

How can you grow a tree made out of crystals?

Remember, the crystallization of a solute from solution is a physical change that is different from freezing.

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Solution Formation

What factors affect how fast a substance dissolves?

Solution Formation

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Solution Formation

Granulated sugar dissolves faster than sugar cubes, and both granulated sugar and sugar cubes dissolve faster in hot tea or when you stir the tea.

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Solution Formation

The compositions of the solvent and the solute determine whether or not a substance will dissolve.

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Solution Formation

Factors that affect how fast a substance dissolves include:

The compositions of the solvent and the solute determine whether or not a substance will dissolve.

  • Agitation
  • Temperature
  • Particle size of the solute

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Solution Formation

Agitation

If the contents of the glass are stirred, the crystals dissolve more quickly.

  • The dissolving process occurs at the surface of the sugar crystals.
  • Stirring speeds up the process because fresh solvent (the water) is continually brought in contact with the surface of the solute (sugar).

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Solution Formation

Agitation

Agitation (stirring or shaking) affects only the rate at which a solid solute dissolves.

  • It does not influence the amount of solute that will dissolve.
  • An insoluble substance remains undissolved regardless of how vigorously or for how long the solvent/solute system is agitated.

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Solution Formation

Temperature also influences the rate at which a solute dissolves.

  • Sugar dissolves much more rapidly in hot tea than in iced tea.

Temperature

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Solution Formation

At higher temperatures, the kinetic energy of water molecules is greater than at lower temperatures, so the

molecules move faster.

Temperature

  • The more rapid motion of the solvent molecules leads to an increase in the frequency of the force of the collisions between water molecules and the surfaces of the sugar crystals.

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Solution Formation

Particle Size of the Solute

The rate at which a solute dissolves also depends upon the size of the solute particles.

  • The smaller particles in granulated sugar expose a much greater surface area to the colliding water molecules.

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Solution Formation

Particle Size of the Solute

The dissolving process is a surface phenomenon.

  • The more surface area of the solute that is exposed, the faster the rate of dissolving.

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Which of the following will not speed up the rate at which a solid solute dissolves?

A. Increasing the temperature

B. Stirring the mixture

C. Crushing the solute

D. Decreasing the temperature

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Which of the following will not speed up the rate at which a solid solute dissolves?

A. Increasing the temperature

B. Stirring the mixture

C. Crushing the solute

D. Decreasing the temperature

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Solubility

How can you describe the equilibrium in a saturated solution?

Solubility

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Solubility

What is happening in this figure?

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Solubility

What is happening in this figure?

  • Particles move from

the solid into the

solution.

  • Some dissolved particles move from the solution back to the solid.
  • Because these two processes occur at the same rate, no net change occurs in the overall system.

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Solubility

Such a solution is said to be saturated.

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Solubility

Such a solution is said to be saturated.

  • A saturated solution contains the maximum amount of solute for a given quantity of solvent at a constant temperature and pressure.

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Solubility

In a saturated solution, a state of dynamic equilibrium exists between the solution and any undissolved solute, provided that the temperature remains constant.

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Solubility

  • Solubility is often expressed in grams of solute per 100 g of solvent (g/100 g H2O).
  • Sometimes the solubility of a gas is expressed in grams per liter of solution (g/L).

The solubility of a substance is the amount of solute that dissolves in a given quantity of a solvent at a specified temperature and pressure to produce a saturated solution.

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Solubility

  • If additional solute is added to an unsaturated solution, the solute will dissolve until the solution is saturated.

A solution that contains less solute than a saturated solution at a given temperature and pressure is an unsaturated solution.

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Solubility

Some liquids—for example, water and ethanol—are infinitely soluble in each other.

  • Two liquids are miscible if they dissolve in each other in all proportions.

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Solubility

Liquids that are insoluble in each other are immiscible.

  • Oil and water are examples of immiscible liquids.

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The solubility of a substance is often expressed as which of the following?

A. grams of solute per 100 liters of solvent

B. grams of solute per 1 cm3 of solvent

C. grams of solute per 100 grams of solvent

D. grams of solute per 100 grams of solution

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The solubility of a substance is often expressed as which of the following?

A. grams of solute per 100 liters of solvent

B. grams of solute per 1 cm3 of solvent

C. grams of solute per 100 grams of solvent

D. grams of solute per 100 grams of solution

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Factors Affecting Solubility

What factors affect the solubility of a substance?

Factors Affecting Solubility

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Factors Affecting Solubility

Temperature affects the solubility of solid, liquid, and gaseous solutes in a solvent; both temperature and pressure affect the solubility of gaseous solutes.

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Temperature

The solubility of most solid substances increases as the temperature of the solvent increases.

Interpret Graphs

Temperature (°C)

Solubility (g/100g H2O)

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  • For a few substances, solubility decreases with temperature.

Temperature

The solubility of most solid substances increases as the temperature of the solvent increases.

Interpret Graphs

Temperature (°C)

Solubility (g/100g H2O)

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0.0

0.076

0.169

0.335

CO2

Carbon dioxide

0.0

0.0026

0.0043

0.0070

O2

Oxygen

0.0

0.00013

0.00016

0.00019

H2

Hydrogen

487

260.4

230.9

179

C12H22O11

Sucrose (table sugar)

733

455.0

222.0

122

AgNO3

Silver nitrate

33.32

31.60

31.03

30.84

AlCl3

Aluminum chloride

182

114.0

88.0

74

NaNO3

Sodium nitrate

39.2

37.0

36.0

35.7

NaCl

Sodium chloride

57.6

42.6

34.0

27.6

KCl

Potassium chloride

56.0

19.3

7.4

4.0

KClO3

Potassium chlorate

0.07

—

0.173

0.189

Ca(OH)2

Calcium hydroxide

—

0.00034

0.00025

0.00019

BaSO4

Barium sulfate

—

—

31.89

1.67

Ba(OH)2

Barium hydroxide

100°C

50°C

20°C

0°C

Formula

Substance

Solubility (g/100 g H2O)

Solubilities of Substances in Water at Various Temperatures

Interpret Data

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Factors Affecting Solubility

  • The crystallization of a supersaturated solution can be initiated if a very small crystal, called a seed crystal, of the solute is added.

A supersaturated solution contains more solute than it can theoretically hold at a given temperature.

Temperature

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Factors Affecting Solubility

The rate at which excess solute deposits upon the surface of a seed crystal can be very rapid.

The solution is clear before a seed crystal is added.

Crystals begin to form immediately after the addition of a seed crystal.

Excess solute crystallizes rapidly.

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CHEMISTRY & YOU

How do you think crystal-growing kits work? Use what you know about solubility and supersaturated solutions to explain your answer.

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CHEMISTRY & YOU

How do you think crystal-growing kits work? Use what you know about solubility and supersaturated solutions to explain your answer.

Crystal-growing kits usually begin with a supersaturated solution. When a seed crystal is added to the solution, crystals rapidly begin to grow because the supersaturated solution contains more solute than is theoretically possible.

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Factors Affecting Solubility

The effect of temperature on the solubility of gases in liquid solvents is opposite that of solids.

  • The solubilities of most gases are greater in cold water than in hot.

Temperature

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Factors Affecting Solubility

  • Gas solubility increases as the partial pressure of the gas above the solution increases.

Changes in pressure have little effect on the solubility of solids and liquids, but pressure strongly influences the solubility of gases.

Pressure

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Factors Affecting Solubility

  • These drinks contain large amounts of carbon dioxide (CO2) dissolved in water.
  • Dissolved CO2 makes the liquid fizz and your mouth tingle.

Pressure

Carbonated beverages are a good example.

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Factors Affecting Solubility

  • The drinks are bottled under a high pressure of CO2 gas, which forces larger amounts of the gas into solution.

Pressure

Carbonated beverages are a good example.

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Factors Affecting Solubility

  • When the container is opened, the partial pressure of CO2 above the liquid decreases.
  • Immediately, bubbles of CO2 form in the liquid and escape from the open bottle.

Pressure

Carbonated beverages are a good example.

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Factors Affecting Solubility

How is the partial pressure of carbon dioxide gas related to the solubility of CO2 in a carbonated beverage?

Pressure

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Factors Affecting Solubility

How is the partial pressure of carbon dioxide gas related to the solubility of CO2 in a carbonated beverage?

  • The relationship is described by Henry’s law, which states that at a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid.

Pressure

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Factors Affecting Solubility

  • As the pressure of the gas above the liquid increases, the solubility of the gas increases.
  • As the pressure of the gas decreases, the solubility of the gas decreases.

Pressure

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Factors Affecting Solubility

You can write the relationship in the form of an equation.

=

S1

P1

S2

P2

  • S1 is the solubility of a gas at one pressure, P1.
  • S2 is the solubility at another pressure, P2.

Pressure

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If the solubility of a gas in water is 0.77 g/L at 3.5 atm of pressure, what is its solubility (in g/L) at 1.0 atm of pressure? (The temperature is held constant at 25°C.)

Sample Problem 16.1

Using Henry’s Law

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KNOWNS

UNKNOWN

S2 = ? g/L

Analyze List the knowns and the unknown.

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Sample Problem 16.1

Use Henry’s law to solve for the unknown solubility.

P1 = 3.5 atm

S1 = 0.77 g/L

P2 = 1.0 atm

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  • State the equation for Henry’s law.

Calculate Solve for the unknowns.

2

Sample Problem 16.1

  • Solve Henry’s law for S2. Substitute the known values and calculate.

=

S1

P1

S2

P2

Isolate S2 by multiplying both sides by P2:

P2 × = × P2

S1

P1

S2

P2

S2 = = = 0.22 g/L

S1 × P2

P1

0.77 g/L × 1.0 atm

3.5 atm

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  • The new pressure is approximately one-third of the original pressure.
  • So, the new solubility should be approximately one-third of the original.
  • The answer is correctly expressed to two significant figures.

Evaluate Does the result make sense?

3

Sample Problem 16.1

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Explain why an opened container of a carbonated beverage is more likely to go flat sitting on the counter than in the refrigerator.

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Explain why an opened container of a carbonated beverage is more likely to go flat sitting on the counter than in the refrigerator.

The solubility of a gas in a liquid increases with decreasing temperature. More carbon dioxide will remain in solution at the colder temperature found in the refrigerator.

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Key Concepts

Factors that determine how fast a substance dissolves are stirring, temperature, and surface area.

In a saturated solution, a state of dynamic equilibrium exists between the solution and any undissolved solute, provided that the temperature remains constant.

Temperature affects the solubility of solid, liquid, and gaseous solutes in a solvent; both temperature and pressure affect the solubility of gaseous solutes.

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Key Equation

Henry’s law: =

S1

P1

S2

P2

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Glossary Terms

  • saturated solution: a solution containing the maximum amount of solute for a given amount of solvent at a constant temperature and pressure; an equilibrium exists between undissolved solute and ions in solution
  • solubility: the amount of a substance that dissolves in a given quantity of solvent at specified conditions of temperature and pressure to produce a saturated solution

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Glossary Terms

  • unsaturated solution: a solution that contains less solute than a saturated solution at a given temperature and pressure
  • miscible: describes liquids that dissolve in each other in all proportions
  • immiscible: describes liquids that are insoluble in each other; oil and water are immiscible

​

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Glossary Terms

  • supersaturated solution: a solution that contains more solute than it can theoretically hold at a given temperature; excess solute precipitates if a seed crystal is added
  • Henry’s law: at a given temperature, the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid

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END OF 16.1

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