Solutions: Properties, Types, and Solubility (Chapter 9 Study Notes)

Core Chemistry Skills From Previous Lectures

Overview

This section reviews essential concepts for understanding solutions in chemistry, including molecular polarity, intermolecular forces, ionic and molecular compounds, and chemical reactions and stoichiometry. These foundational topics are critical for predicting solubility and the behavior of substances in solution.

• Molecular Polarity: Refers to the distribution of electrical charge over the atoms in a molecule (Chapter 6.8).

• Intermolecular Forces: Includes ion-dipole, hydrogen bonding, dipole-dipole, and dispersion forces (Chapter 6.9).

• Ionic and Molecular Compounds: Naming and formulas (Chapter 6).

• Chemical Reactions and Stoichiometry: Quantitative relationships in chemical reactions (Chapter 7.1).

Example: The reaction AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) demonstrates the formation of a precipitate in aqueous solution.

Aqueous (aq) solution means dissolved in water.

Chapter 9: Solutions

Introduction to Solutions

Solutions are homogeneous mixtures of two or more substances. They are ubiquitous in daily life and laboratory settings, including medical IV fluids, seawater, laboratory reagents, sports drinks, lemonade, and chemical reactions.

Solutions (Section 9.1)

Definition and Components

A solution is a homogeneous mixture of two or more substances. Solutions have two main components:

• Solvent: Present in a larger amount; the major component.

• Solute(s): Present in smaller amount(s); the substance(s) dissolved.

Equation: solute(s) + solvent → solution

Solutes

Solutes are the smaller amounts of dissolved substances in a solution. They can be solids, liquids, or gases and are dispersed evenly throughout the solution. Solutes:

• Cannot be separated from solution by filtration, but can be separated by physical or chemical means (e.g., evaporation).

• Are not visible as particles but can color the solution.

Examples: NaCl in saline solution, CuSO4 in copper(II) sulfate solution, CO2 gas in sparkling water, isopropyl alcohol in rubbing alcohol.

Solvent

The solvent is the major component of a solution. Solvent molecules have sufficient intermolecular interactions with solute particles to dissolve the solute. Water, a polar molecule with polar O-H bonds, is one of the most common solvents.

• Solvent molecules interact with solute via ion-dipole, hydrogen bonding, or dipole-dipole interactions.

Water as Solvent

Most chemical and biochemical reactions occur in water as the solvent. The human body is 45-75% water by mass, with infants having up to 74%. Reactions in water are called aqueous reactions. The label (aq) identifies compounds/ions dissolved in water.

Types of Solutes and Solvents

Classification

Solutes and solvents may be solids, liquids, or gases. The following table summarizes examples:

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

Predicting Solubility: "Like Dissolves Like"

Polarity and Solubility

Solutions form when the solute and solvent have similar polarities. The principle "like dissolves like" means:

• Polar solute dissolves in polar solvent (e.g., water, acetone, ethanol).

• Nonpolar solute dissolves in nonpolar solvent (e.g., hexane, toluene, carbon tetrachloride).

Solutions Will Form	Solutions Will Not Form
Polar solute + Polar solvent	Polar solute + Nonpolar solvent
Nonpolar solute + Nonpolar solvent	Nonpolar solute + Polar solvent

Examples of polar solutes: Ionic compounds (NaCl, KNO3), acetone, ethanol.

Examples of nonpolar solutes: Hydrocarbons, oils, fats, iodine (I2).

Non-Polar Molecules

Non-polar molecules such as butane, hexane, toluene, palmitic acid, carbon tetrachloride, bromine, and iodine dissolve better in non-polar solvents because their non-polar portion outweighs any polar portion.

Non-Polar Solutes Do Not Dissolve in Polar Solvents

Non-polar molecules do not dissolve in water due to the lack of intermolecular attraction between non-polar solute and polar solvent. Examples include oils, fats, fat-soluble vitamins (A, D), and hydrocarbon compounds.

Practice: Like Dissolves Like

Question: Which substance would most likely dissolve in toluene (C7H8), a nonpolar solvent?

• A. Water (H2O)

• B. Sodium sulfate (Na2SO4)

• C. Octane (C8H18) ← Correct

• D. Sodium chloride (NaCl)

Ionic Solutes Dissolve in Water via Ion-Dipole Interactions

Mechanism

Ionic solutes (e.g., NaCl) form ion-dipole interactions with water. Water molecules surround and separate the ions, pulling them into solution.

Equation: $\text{NaCl}(s) \xrightarrow{H_2O} \text{Na}^+(aq) + \text{Cl}^-(aq)$

Examples:

• $\text{CaBr}_2(s) \xrightarrow{H_2O} \text{Ca}^{2+}(aq) + 2\text{Br}^-(aq)$

• $\text{AgNO}_3(s) \xrightarrow{H_2O} \text{Ag}^+(aq) + \text{NO}_3^-(aq)$

Ionic Solutes Dissociate into Ions

When ionic compounds dissolve in water, they dissociate into their constituent ions. The table below summarizes types and relative amounts of ions formed:

Ionic Compound	Types of Ions Produced	Relative Amounts of Cation	Relative Amounts of Anion
MgBr2	Mg2+, Br-	1 mole Mg2+	2 moles Br-
AlCl3	Al3+, Cl-	1 mole Al3+	3 moles Cl-
Na2SO4	Na+, SO42-	2 moles Na+	1 mole SO42-
K3PO4	K+, PO43-	3 moles K+	1 mole PO43-

Electrolytes and Non-Electrolytes (Section 9.2)

Definitions

• Electrolytes: Solutes that dissociate into ions when dissolved in water. Their solutions conduct electricity due to the presence of hydrated ions.

• Non-Electrolytes: Compounds that do not yield ions in water and do not conduct electricity.

Examples of electrolytes:

• Water-soluble ionic compounds: NaCl, KBr, KOH, Ca(NO3)2, LiOH, MgCl2, CuSO4

• Molecular acids: HCl, H2SO4, HBr, HClO4

Strong vs. Weak Electrolytes

• Strong electrolytes: Dissociate completely (~100%) into ions. Example: $\text{NaCl}(s) \rightarrow \text{Na}^+(aq) + \text{Cl}^-(aq)$

• Weak electrolytes: (Weak acids/bases) Dissociate slightly into ions, resulting in a mixture of ions and molecules. Example: $\text{CH}_3\text{COOH}(aq) \rightleftharpoons \text{H}^+(aq) + \text{CH}_3\text{CO}_2^-(aq)$

The symbol $\rightleftharpoons$ indicates equilibrium.

Non-Electrolytes

Compounds that do not yield ions in water. Examples include ethanol (CH3CH2OH), urea (H2NCONH2), and table sugar (C12H22O11).

Classification Table

Type of Solute	In Solution	Type(s) of Particles	Conducts Electricity?	Examples
Strong electrolyte	Dissociates completely	Ions only	Yes	NaCl, KBr, MgCl2, HCl
Weak electrolyte	Ionizes partially	Mostly molecules, some ions	Weakly	HF, NH3, CH3COOH
Non-electrolyte	No ionization	Molecules only	No	CH3OH, C12H22O11, urea

Solubility of Solutes in a Solvent (Section 9.3)

Definition

Solubility is the maximum amount of solute that dissolves in a specific amount of solvent at a specific temperature. It is often expressed as grams of solute per 100 grams of solvent.

• Example: Solubility of NaCl is 36 g per 100 g water at 25°C (very soluble).

• Example: Solubility of CaCO3 is ~15 mg per 100 g water at 25°C (not very soluble).

Unsaturated Solutions

Contain less than the maximum amount of solute (below solubility limit). No undissolved solute is present. Additional solute will dissolve until the maximum is reached.

Saturated Solutions

Contain the maximum amount of solute that can dissolve at a specific temperature. Undissolved solute is present at the bottom. Solute dissolving and crystallizing occur in a dynamic equilibrium process.

Equation: solute + solvent → saturated solution (at equilibrium: solute dissolves ↔ solute crystallizes)

Summary Table: Types of Solutions

Mixture Type	Particle Size	Settling	Separation
Solution	Small particles	No settling	Cannot be separated by filtration
Colloid	Medium particles	No settling	Can be separated by semipermeable membranes
Suspension	Large particles	Particles settle	Can be separated by filtration

Additional info: These notes cover the fundamental properties of solutions, types of solutes and solvents, the principle of "like dissolves like," mechanisms of dissolution, and the classification of electrolytes and non-electrolytes, as well as the concept of solubility and saturation. These concepts are essential for understanding chemical reactions in aqueous media and predicting the behavior of substances in biological and laboratory contexts.