General Properties of Solutions

Definition and Components

Solutions are homogeneous mixtures of two or more pure substances. The solvent is the substance present in greatest abundance, typically a liquid, while solutes can be solids, liquids, or gases. When water is the solvent, the solution is termed an aqueous solution.

• Solvent: Major component, usually a liquid.

• Solute: Minor component, can be solid, liquid, or gas.

• Aqueous solution: Water acts as the solvent.

Example: Sodium chloride (NaCl) dissolved in water forms an aqueous solution.

Dissolution of Ionic and Molecular Compounds

When ionic compounds dissolve in water, their ions dissociate and become surrounded by water molecules, forming solvated ions. Molecular compounds, such as methanol, dissolve without forming ions.

• Ionic compounds: Dissociate into ions (e.g., NaCl → Na+ and Cl-).

• Molecular compounds: Dissolve as intact molecules (e.g., CH3OH).

Electrolytic Properties

Types of Electrolytes

Electrolytes are substances whose aqueous solutions conduct electricity due to the presence of ions. They are classified as:

• Strong Electrolytes: Dissociate completely in water, producing many ions and conducting electricity well. Examples: NaCl, KBr, strong acids and bases.

• Weak Electrolytes: Partially dissociate, producing fewer ions and conducting poorly. Examples: CH3COOH, NH3.

• Nonelectrolytes: Do not produce ions; their solutions do not conduct electricity. Examples: sugar, methanol.

Example: The three beakers below illustrate strong, weak, and nonelectrolyte solutions.

Precipitation Reactions

Formation of Precipitates

A precipitation reaction occurs when two solutions of soluble ionic compounds are mixed and an insoluble product (precipitate) forms. The solubility of a substance is the maximum amount that can dissolve in a given quantity of solvent at a specific temperature.

• Insoluble: Solubility < 0.01 mol/L; forms a solid precipitate.

• Soluble: Dissolves readily in water.

Example: Mixing Pb(NO3)2 and KI forms PbI2 precipitate.

Solubility Rules

Solubility rules help predict whether a compound will dissolve in water or form a precipitate. Tables below summarize common soluble and insoluble ionic compounds and their exceptions.

Exchange (Metathesis) Reactions

Mechanism and Balancing

Exchange reactions involve the swapping of ions between two soluble ionic compounds, often resulting in a precipitate. The general form is:

Steps to balance:

1. Identify ions present in reactants.

2. Combine cations and anions to form products, checking charges.

3. Use solubility rules to determine if a product is insoluble.

4. Balance the equation.

Ionic Equations

Molecular, Complete Ionic, and Net Ionic Equations

• Molecular Equation (ME): Shows all reactants and products in their complete chemical forms.

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

• Net Ionic Equation (NIE): Shows only the species that change during the reaction; spectator ions are omitted.

Example: For AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq):

• ME: AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)

• CIE: Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) → AgCl(s) + K+(aq) + NO3-(aq)

• NIE: Ag+(aq) + Cl-(aq) → AgCl(s)

Acids and Bases

Bronsted-Lowry Definition

• Acid: Donates H+ to another substance.

• Base: Accepts H+ from another substance.

• Neutralization: Reaction between an acid and a base.

In water:

• Acids increase H+ concentration.

• Bases increase OH- concentration.

Strong acids and bases: Dissociate completely in water.

Neutralization Reactions and Salts

Formation of Salts and Water

A neutralization reaction occurs when an acid reacts with a base, producing a salt and water.

Net ionic equation for strong acid and base:

Concentrations of Solutions

Molarity

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

Example: Calculate the molarity of a solution containing 5.30 moles of CuSO4 in 0.750 L:

Expressing the Concentration of an Electrolyte

Ion Concentrations in Solution

When ionic compounds dissolve, the concentration of each ion depends on the formula.

• 1 mol NaCl → 1 mol Na+ and 1 mol Cl-

• 1 M NaCl solution → 1 M Na+ and 1 M Cl-

Example: 1 M Na2SO4 solution gives 2 M Na+ and 1 M SO42-.

Mass-Related Concentrations: Mass Percentage, ppm, and ppb

Definitions and Calculations

• Mass %:

• ppm:

• ppb:

Example: Dissolving 0.268 g glucose in 2.50 g water: mass % =

Dilutions

Principle and Calculation

Dilution involves adding solvent to a solution to decrease its concentration. The number of moles of solute remains constant.

Example: How many mL of 4.0 M AgNO3 are needed to make 320 mL of 0.2 M AgNO3?

Solution Stoichiometry and Chemical Analysis

Stoichiometry in Solution Reactions

• Write a balanced reaction equation.

• Convert mass or concentration to moles:

• Use molar ratios to relate reactants and products.

• Calculate mass or concentration as required.

Example: What mass of NaOH is needed to precipitate Cd2+ ions from 20.0 mL of 0.100 M Cd(NO3)2?

• Step 1: Calculate moles of Cd2+

• Step 2: Use molar ratio to find moles of NaOH

• Step 3: Find mass of NaOH

Summary Table: Strong Acids and Bases

*Additional info: Academic context and examples were added to clarify and expand upon brief points in the original material.*