Chapter 13: Solutions – Study Notes for Introductory Chemistry

Chapter 13: Solutions

Introduction to Solutions

Solutions are homogeneous mixtures composed of two or more substances. They are fundamental in chemistry and are encountered in everyday life, from ocean water to blood plasma. Understanding solutions involves exploring their composition, properties, and the factors affecting solubility.

Tragedy in Cameroon: Chemistry in Context

Case Study: Lake Nyos Disaster

• Background: In 1986, a sudden release of carbon dioxide from Lake Nyos in Cameroon resulted in the deaths of over 1700 people and 3000 cattle. A similar event occurred at Lake Monoun in 1984.

• Chemical Cause: Molten volcanic rock beneath the lake produced carbon dioxide, which dissolved in the lake water under high pressure, forming a concentrated solution.

• Physical Process: The release of pressure caused the dissolved gas to come out of solution rapidly, forming a deadly cloud.

• Prevention: Scientists installed a venting system to gradually release CO2 and prevent future disasters.

Solutions: Homogeneous Mixtures

Definition and Examples

• A solution is a homogeneous mixture of two or more substances.

• Common examples include ocean water (salt in water), blood plasma (solids and gases in water), and soda water (CO2 in water).

• Solutions can involve combinations of gases, liquids, and solids.

Components of a Solution

• The solvent is the majority component; the solute is the minority component.

• In aqueous solutions, water is the solvent.

• Other solvents are used for nonpolar solutes in labs and industry.

Common Types of Solutions

Solution Phase	Solute Phase	Solvent Phase	Example
Gaseous solutions	Gas	Gas	Air (mainly O2 and N2)
Liquid solutions	Gas	Liquid	Soda water (CO2 and water)
Liquid solutions	Liquid	Liquid	Vodka (ethanol and water)
Liquid solutions	Solid	Liquid	Seawater (salt and water)
Solid solutions	Solid	Solid	Brass (copper and zinc)

Common Solvents

Common Polar Solvents	Common Nonpolar Solvents
Water (H2O)	Hexane (C6H14)
Acetone (CH3COCH3)	Diethyl ether (CH3CH2OCH2CH3)
Methyl alcohol (CH3OH)	Toluene (C7H8)

• Like dissolves like: Polar solvents dissolve polar solutes; nonpolar solvents dissolve nonpolar solutes.

How a Solid Dissolves in Water

Process of Dissolution

• When a solid is placed in water, there is competition between solute-solute, solvent-solvent, and solvent-solute attractions.

• If solvent-solute attractions are stronger, the solid dissolves.

• Example: For NaCl, water dipoles surround and separate Na+ and Cl- ions, dispersing them throughout the solution.

Solubility and Saturation

Definitions

• Solubility: The amount of a compound (in grams) that dissolves in a certain amount of liquid.

• Saturated solution: Contains the maximum amount of solute under given conditions.

• Unsaturated solution: Contains less than the maximum amount of solute; more solute can dissolve.

• Supersaturated solution: Contains more than the normal maximum amount of dissolved solute; excess solute will precipitate out.

Factors Affecting Solubility

• Solubility of solids in water generally increases with temperature.

• Solubility of gases in water decreases with increasing temperature but increases with increasing pressure.

Solubility of Different Substances

• Ionic solids: Solubility depends on the relative strength of solute-solute and solvent-solute attractions (e.g., CaCO3 is insoluble in water).

• Molecular solids: Polar molecular solids (e.g., sugar) are soluble in water; nonpolar solids (e.g., lard) are not.

Electrolyte and Nonelectrolyte Solutions

• Electrolyte solutions: Contain dissolved ions and conduct electricity (e.g., salt solution).

• Nonelectrolyte solutions: Contain dissolved molecules and do not conduct electricity (e.g., sugar solution).

Temperature Dependence of Solubility

• Solubility of solids increases with temperature (e.g., more potassium nitrate dissolves at higher temperatures).

• Solubility of gases decreases with temperature (e.g., warm soda loses carbonation faster).

Purification by Recrystallization

• Recrystallization: A technique to purify solids by dissolving them at high temperature and allowing them to crystallize as the solution cools, leaving impurities behind.

• Example: Making rock candy by cooling a saturated sugar solution and allowing crystals to form on a string.

Solutions of Gas in Water

• Many liquids contain dissolved gases (e.g., oxygen in lake water, CO2 in soda).

• Solubility of gases decreases with increasing temperature and increases with pressure (Henry's Law).

Summary Table: Solution Properties

Property	Solids in Liquids	Gases in Liquids
Effect of Temperature	Solubility increases	Solubility decreases
Effect of Pressure	Little effect	Solubility increases

Key Equations

• Mass Percent: $\text{mass percent} = \frac{\text{mass solute}}{\text{mass solute} + \text{mass solvent}} \times 100$

• Molarity (M): $\text{molarity (M)} = \frac{\text{moles solute}}{\text{liters solution}}$

• Dilution Equation: $M_1V_1 = M_2V_2$

Learning Objectives

• Define solution, solute, and solvent.

• Relate solubility of solids and gases to temperature and pressure.

• Calculate mass percent and molarity.

• Use dilution equations and stoichiometry in solution calculations.