Solutions, Electrolytes, Acids, Bases, and Solubility in Aqueous Chemistry

Solutions and Solution Vocabulary

Definitions and Key Concepts

Understanding the nature of solutions is fundamental in general chemistry, especially when dealing with aqueous (water-based) systems. Below are essential terms and their explanations:

• Solution: A homogeneous mixture composed of two or more substances, where the composition is uniform throughout. It consists of a solvent and one or more solutes.

• Solvent: The component present in the larger amount; in general chemistry, this is typically H2O (water).

• Solute: The component present in the smaller amount; the substance that is dissolved in the solvent.

• Solubility: The maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature.

• Molarity (M): A common unit of concentration, defined as moles of solute per liter of solution: $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

• Percent by mass: $\frac{\text{mass of solute}}{\text{mass of solution}} \times 100\%$

• Parts per million (ppm): $\frac{\text{mg of solute}}{\text{kg of solvent}}$

• Dilute solution: Contains a small amount of solute relative to the solvent.

• Concentrated solution: Contains a large amount of solute relative to the solvent.

Examples

• Example 1: How many moles of HCl are present in 320 mL of 0.250 M HCl? $0.250~\text{mol/L} \times 0.320~\text{L} = 0.080~\text{mol HCl}$

• Example 2: What is the concentration of a solution with 9.0 g of ammonium dichromate in 500 mL of solution? $\frac{9.0~\text{g}}{252.07~\text{g/mol}} = 0.036~\text{mol}$ $\frac{0.036~\text{mol}}{0.500~\text{L}} = 0.072~\text{M}$

Types of Solutions and Dissolution

Solubility and Dissolution Process

When a solid dissolves in water, the process involves breaking the solute's intermolecular forces and forming new interactions between solute and solvent particles. The dissolution of ionic compounds results in the formation of ions that are free to move in solution, allowing the solution to conduct electricity.

• Ionic compounds: Dissolve by dissociation into their constituent ions (e.g., NaCl(s) → Na+(aq) + Cl-(aq)).

• Molecular compounds: Dissolve without forming ions (e.g., sucrose(s) → sucrose(aq)).

Factors Affecting Solubility

• Nature of solute and solvent ("like dissolves like")

• Temperature

• Pressure (for gases)

Electrolytes: Strong, Weak, and Nonelectrolytes

Definitions

• Electrolyte: A substance that produces ions in aqueous solution and conducts electricity.

• Strong Electrolyte: Completely dissociates into ions (e.g., soluble salts, strong acids, strong bases).

• Weak Electrolyte: Partially dissociates into ions (e.g., weak acids, weak bases).

• Nonelectrolyte: Does not produce ions in solution (e.g., most molecular compounds like sugar).

How to Identify

• Strong electrolytes: Soluble ionic compounds, strong acids, and strong bases.

• Weak electrolytes: Weak acids and bases, slightly soluble salts.

• Nonelectrolytes: Molecular compounds that do not ionize in water.

Acids, Bases, and Salts

Definitions and Theories

• Arrhenius Theory:

  • Acid: Produces H+ (or H3O+) ions in aqueous solution.

  • Base: Produces OH- ions in aqueous solution.

• Brønsted-Lowry Theory:

  • Acid: Proton (H+) donor.

  • Base: Proton (H+) acceptor.

• Lewis Theory:

  • Acid: Electron pair acceptor.

  • Base: Electron pair donor.

Strong and Weak Acids/Bases

• Strong acids/bases: Ionize or dissociate nearly 100% in solution.

• Weak acids/bases: Only partially ionize or dissociate.

Common Strong Acids and Bases

Strong Acids	Strong Bases
HCl (Hydrochloric acid)	LiOH (Lithium hydroxide)
HBr (Hydrobromic acid)	NaOH (Sodium hydroxide)
HI (Hydroiodic acid)	KOH (Potassium hydroxide)
HNO3 (Nitric acid)	RbOH (Rubidium hydroxide)
HClO4 (Perchloric acid)	CsOH (Cesium hydroxide)
H2SO4 (Sulfuric acid)	Ca(OH)2 (Calcium hydroxide)
	Sr(OH)2 (Strontium hydroxide)
	Ba(OH)2 (Barium hydroxide)

Salts

• Salt: An ionic compound whose cation is not H+ and anion is not OH-.

• Formed as the product of an acid-base reaction.

• Composed of metal cations and non-metal anions.

Solubility Rules

General Solubility Rules for Ionic Compounds in Water

Ion	Soluble	Insoluble	Exceptions
Group 1 Salts	Always Soluble
NO3-, ClO4-	Always Soluble
Cl-, Br-, I-	Usually Soluble		Ag+, Pb2+, Hg22+
SO42-	Usually Soluble		Ca2+, Sr2+, Ba2+, Pb2+
CO32-, PO43-		Usually Insoluble	Group 1, NH4+
OH-		Usually Insoluble	Group 1, Ca2+, Sr2+, Ba2+

Dilution and Solution Preparation

Dilution Calculations

Dilution involves adding solvent to a solution to decrease its concentration. The relationship between the concentrations and volumes before and after dilution is given by:

$M_1 V_1 = M_2 V_2$

• $M_1$ = initial (concentrated) molarity

• $V_1$ = initial volume

• $M_2$ = final (dilute) molarity

• $V_2$ = final volume

Example: You need 150.0 mL of 0.500 M HCl, and you have 12.0 M HCl. What volume of concentrated HCl do you use?

$0.500~\text{M} \times 0.150~\text{L} = 12.0~\text{M} \times V_1$ $V_1 = \frac{0.500 \times 0.150}{12.0} = 0.00625~\text{L} = 6.25~\text{mL}$

Electrolyte Conductivity and Identification

Conductivity in Solution

• Substances that form ions in aqueous solution conduct electricity.

• Strong electrolytes (soluble salts, strong acids/bases) conduct well.

• Weak electrolytes (weak acids/bases, slightly soluble salts) conduct poorly.

• Nonelectrolytes (e.g., sugar) do not conduct electricity.

Summary Table: Electrolyte Types

Type	Definition	Examples	Conductivity
Strong Electrolyte	Completely dissociates into ions	NaCl, HCl, NaOH	High
Weak Electrolyte	Partially dissociates into ions	CH3COOH, NH3	Low
Nonelectrolyte	Does not form ions	Sucrose, ethanol	None

Practice and Application

• Be able to write dissociation equations for ionic compounds in water.

• Use solubility rules to predict precipitation reactions.

• Calculate solution concentrations using molarity, percent by mass, and ppm.

• Perform dilution calculations using $M_1 V_1 = M_2 V_2$.

Additional info: Some diagrams and sketches referenced in the notes are not included here, but students are encouraged to visualize the particulate nature of solutions (e.g., ions dispersed in water, molecular compounds remaining intact).