Chapter 9: Solutions – GOB Chemistry Study Notes

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Chapter 9: Solutions

Introduction

This chapter explores the fundamental concepts of solutions in chemistry, including their definitions, types, properties, and biological relevance. Solutions are essential in both chemical and biological systems, affecting processes such as dialysis and cellular water regulation.

Learning Objectives

Define solutions and solubility
Write equations for the dissolution of strong and weak electrolytes
Calculate mass, volume, and mass/volume % concentrations of solutions
Define molarity
Differentiate between solutions and colloids
Define osmosis and dialysis

Basic Definitions

Solutions

A solution is a homogeneous mixture of two or more substances. Solutions form when there is sufficient attraction between solute and solvent molecules. They consist of two components:

Solvent: The substance present in greater amount.
Solute: The substance present in lesser amount.

Example: In salt water, water is the solvent and salt (NaCl) is the solute.

Types of Solutions

Classification by Physical State

Solutions can exist in various combinations of solid, liquid, and gas phases. The following table summarizes common types:

Type	Example	Solute	Solvent
Gas in Gas	Air	O2(g)	N2(g)
Gas in Liquid	Soda water	CO2(g)	H2O(l)
Liquid in Liquid	Vinegar	HC2H3O2(l)	H2O(l)
Solid in Liquid	Seawater	NaCl(s)	H2O(l)
Solid in Solid	Brass	Zn(s)	Cu(s)

Additional info: Solutions can also be formed with other combinations, such as gas in solid or liquid in solid.

Solubility

Definition and Factors

Solubility is the maximum amount of solute that can dissolve in a specific amount of solvent at a given temperature. It is usually expressed as grams of solute per 100 g of solvent (commonly water).

Temperature affects solubility: Most solids are more soluble at higher temperatures.
"Like dissolves like": Polar solutes dissolve in polar solvents; nonpolar solutes dissolve in nonpolar solvents.

Example: Methanol (a polar molecule) dissolves in water due to hydrogen bonding.

Electrolytes and Nonelectrolytes

Definitions

Electrolytes: Substances that dissociate into ions in water, conducting electricity.
Nonelectrolytes: Substances that dissolve as molecules and do not conduct electricity.

Strong Electrolytes

Dissociate 100% in water, producing positive and negative ions.
Conduct electric current strongly.

Example equation:

Weak Electrolytes

Dissociate only slightly in water.
Form solutions with few ions and mostly undissociated molecules.

Example equation:

Nonelectrolytes

Dissolve as molecules in water.
Do not produce ions or conduct electricity.

Saturated and Unsaturated Solutions

Definitions

Unsaturated Solution: Contains less than the maximum amount of solute; more solute can dissolve.
Saturated Solution: Contains the maximum amount of solute; undissolved solute may be present.

Concentration of Solutions

General Formula

The concentration of a solution is the amount of solute divided by the amount of solution. Units may include grams, milliliters, or moles.

General formula:

Mass Percent (m/m)

Mass percent expresses the mass of solute per mass of solution, multiplied by 100%.

Formula:

Example: Dissolving 30.0 g NaOH in 120.0 g H2O yields:

Volume Percent (v/v) and Mass/Volume Percent (m/v)

Volume percent (v/v): Percent volume (mL) of solute to volume (mL) of solution.
Mass/volume percent (m/v): Percent mass (g) of solute to volume (mL) of solution.

Molarity

Definition

Molarity (M) is defined as the moles of solute per liter of solution.

Formula:

Example: A 1.0 M NaCl solution contains 1.0 mole NaCl per 1 L solution.

Solutions, Colloids, and Suspensions

Comparison Table

Mixture Type	Particle Size	Settling	Separation by Membrane
Solution	Small (atoms, ions, molecules)	Do not settle	Cannot be separated by semipermeable membranes
Colloid	Larger molecules or groups	Do not settle	Can be separated by filters, not by semipermeable membranes
Suspension	Very large particles	Settle rapidly	Can be separated by filters

Examples of Colloids

Colloid Type	Dispersed Substance	Dispersing Medium
Fog, hairsprays	Liquid	Gas
Whipped cream, soap foam	Gas	Liquid
Mayonnaise, homogenized milk	Liquid	Liquid
Butter, cheese	Solid	Liquid
Plasma, paints, gelatin	Solid	Liquid

Osmosis and Dialysis

Osmosis

Osmosis is the flow of solvent (usually water) through a semipermeable membrane from a region of lower solute concentration to higher solute concentration. Water moves until concentrations equalize.

Tonicity in Biological Systems

Isotonic solution: Same osmotic pressure as body fluids; no net water movement. Example: 0.90% (m/v) NaCl or 5.0% (m/v) glucose.
Hypotonic solution: Lower solute concentration than cells; water enters cells, causing swelling and possible bursting (hemolysis).
Hypertonic solution: Higher solute concentration than cells; water leaves cells, causing shrinkage (crenation).

Dialysis

Dialysis is the process by which waste products and excess water are removed from the blood through a semipermeable membrane, allowing only small molecules to pass.

Additional info: These concepts are foundational for understanding chemical and biological processes involving solutions, such as intravenous therapy, cellular homeostasis, and laboratory techniques.