General Properties of Aqueous Solutions

Definition and Components

Solutions are homogeneous mixtures composed of two or more pure substances. The solvent is the component present in the greatest amount, while solutes are the substances dissolved in the solvent. For example, in a sugar-water solution, water is the solvent and sugar is the solute.

Electrolytic Properties

Electrolytes vs. Nonelectrolytes

Substances that produce ions in aqueous solution are called electrolytes (e.g., NaCl), while those that do not form ions are nonelectrolytes (e.g., C12H22O11). Electrolytes conduct electricity due to the movement of ions, whereas nonelectrolytes do not.

• Electrolyte: Substance whose aqueous solution conducts electricity (e.g., NaCl).

• Nonelectrolyte: Substance whose aqueous solution does not conduct electricity (e.g., sucrose).

Ionic Compounds in Water

Dissociation and Solvation

When ionic compounds dissolve in water, they dissociate into their constituent ions, which are then surrounded by water molecules in a process called solvation. This prevents the ions from recombining and allows them to move freely in solution.

• Dissociation: Separation of ions from the solid structure into solution.

• Solvation: Surrounding of ions by water molecules, stabilizing them in solution.

Example equation:

Water as an Effective Solvent

Polarity of Water

Water is an electrically neutral molecule but is highly effective at dissolving ionic compounds due to its polarity. The oxygen atom carries a partial negative charge (δ−), while the hydrogen atoms carry partial positive charges (δ+), allowing water to interact with both cations and anions.

Molecular Compounds in Water

Dissolution Without Ionization

Molecular compounds, such as methanol (CH3OH), typically dissolve in water as intact molecules without forming ions. Thus, their solutions do not conduct electricity and are classified as nonelectrolytes.

Ionic vs. Molecular Compounds

Classification and Exceptions

• Ionic Compounds: Consist of metals and non-metals (e.g., NaCl, KCN).

• Molecular Compounds: Consist of non-metals only (e.g., CH3OH, C12H22O11).

• Some molecular substances, such as HCl, ionize in water and behave as acids.

• Ammonium ion (NH4+) acts as a pseudo-alkali metal ion; compounds containing NH4+ are considered ionic.

Strong and Weak Electrolytes

Degree of Ionization

• Strong Electrolytes: Completely or nearly completely ionize in solution (e.g., NaCl).

• Weak Electrolytes: Partially ionize in solution, with most molecules remaining intact (e.g., CH3COOH).

Example equations:

• Strong: (100% ionization)

• Weak: (1% ionization)

Precipitation Reactions

Formation of Insoluble Products

Precipitation reactions occur when two aqueous solutions combine to form an insoluble solid, called a precipitate. This happens when pairs of oppositely charged ions attract each other strongly enough to form an insoluble ionic solid.

Example equation:

Solubility Guidelines for Ionic Compounds

Predicting Solubility

The solubility of a substance is the amount that can dissolve in a given quantity of solvent at a specific temperature. Substances with solubility less than 0.01 mol/L are considered insoluble. The following table summarizes the solubility rules for common ionic compounds:

Exchange (Metathesis) Reactions

Double Replacement Pattern

Exchange (metathesis) reactions involve the exchange of cations and anions between reactants. Precipitation and many neutralization reactions follow this pattern:

General form:

Example:

Ionic Equations

Molecular, Complete Ionic, and Net Ionic Equations

• Molecular Equation: Shows all reactants and products as compounds.

• Complete Ionic Equation: Shows all strong electrolytes as ions.

• Net Ionic Equation: Includes only the species that participate directly in the reaction; spectator ions are omitted.

Example:

• Molecular:

• Complete Ionic:

• Net Ionic:

The sum of ionic charges must be equal on both sides of the equation.

Acids, Bases, and Neutralization Reactions

Definitions and Examples

• Acids: Substances that ionize in water to produce H+ ions (proton donors). Example: HCl, CH3COOH.

• Bases: Substances that accept H+ ions or produce OH− in water. Example: NaOH, NH3.

Example equations:

• Acid:

• Base:

Strong and Weak Acids and Bases

Degree of Ionization

• Strong Acids/Bases: Completely ionize in solution (e.g., HCl, NaOH).

• Weak Acids/Bases: Partially ionize in solution (e.g., CH3COOH, NH3).

Memorize the common strong acids and bases for quick identification.

Neutralization Reactions and Salts

Formation of Water and Salts

Neutralization reactions occur when acids and bases react to form water and a salt. The net ionic equation for a strong acid and strong base is:

Concentrations of Solutions

Molarity and Parts Per Million (ppm)

• Molarity (M):

• ppm:

Example: A 1.00 M solution contains 1.00 mol of solute per liter of solution.

Dilution

Preparation of Solutions of Lower Concentration

Dilution involves adding solvent to a concentrated solution to achieve a desired lower concentration. The relationship is:

Solution Stoichiometry

Calculations Involving Reactions in Solution

Solution stoichiometry uses the volume and concentration of solutions to determine the amounts of reactants and products. Always start with a balanced chemical equation.

Example: How many grams of Ca(OH)2 are needed to neutralize 25.0 mL of 0.100 M HNO3?

• Step 1: Calculate moles of HNO3:

• Step 2: Use stoichiometry to find moles of Ca(OH)2

• Step 3: Convert to grams using molar mass

Additional info: This guide covers the core concepts of reactions in aqueous solution, including electrolytes, precipitation, solubility rules, acid-base reactions, solution concentration, dilution, and stoichiometry, as outlined in a typical General Chemistry curriculum.